Modified factor VIII

ABSTRACT

Specific amino acid loci of human factor VIII interact with inhibitory antibodies of hemophilia patients who have developed such antibodies after being treated with factor VIII. Modified factor VIII is disclosed in which the amino acid sequence is changed by a substitution at one or more of the specific loci. The modified factor VIII is not inhibited by inhibitory antibodies against the A2 or C2 domain epitopes. The modified factor VIII is useful for hemophiliacs, either to avoid or prevent the action of inhibitory antibodies.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/187,319 filed Jun. 28, 2002 which is a continuation-in-partof U.S. patent application Ser. No. 09/523,656 filed Mar. 10, 2000, nowU.S. Pat. No. 6,458,563, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/037,601 filed Mar. 10, 1998, which issued asU.S. Pat. No. 6,180,371; which is a continuation-in-part of U.S. patentapplication Ser. No. 08/670,707 filed Jun. 26, 1996, which issued asU.S. Pat. No. 5,859,204; and of International Patent Application No.PCT/US97/11155 filed Jun. 26, 1997. All of the foregoing priorityapplications are incorporated herein by reference to the extent notinconsistent herewith.

ACKNOWLEDGMENT OF FEDERAL RESEARCH SUPPORT

The government has rights in this invention arising from NationalInstitutes of Health Grant Nos. HL40921, HL46215, and HL36094 thatpartially funded the research leading to this invention.

BACKGROUND OF THE INVENTION

This invention relates generally to a hybrid factor VIII having humanand animal factor VIII amino acid sequence or having human factor VIIIand non-factor VIII amino acid sequence and methods of preparation anduse thereof.

Blood clotting begins when platelets adhere to the cut wall of aninjured blood vessel at a lesion site. Subsequently, in a cascade ofenzymatically regulated reactions, soluble fibrinogen molecules areconverted by the enzyme thrombin to insoluble strands of fibrin thathold the platelets together in a thrombus. At each step in the cascade,a protein precursor is converted to a protease that cleaves the nextprotein precursor in the series. Cofactors are required at most of thesteps.

Factor VIII circulates as an inactive precursor in blood, bound tightlyand non-covalently to von Willebrand factor. Factor VIII isproteolytically activated by thrombin or factor Xa, which dissociates itfrom von Willebrand factor and activates its procoagulant function inthe cascade. In its active form, the protein factor VIIIa is a cofactorthat increases the catalytic efficiency of factor IXa toward factor Xactivation by several orders of magnitude.

People with deficiencies in factor VIII or antibodies against factorVIII who are not treated with factor VIII suffer uncontrolled internalbleeding that may cause a range of serious symptoms, from inflammatoryreactions in joints to early death. Severe hemophiliacs, who numberabout 10,000 in the United States, can be treated with infusion of humanfactor VIII, which will restore the blood's normal clotting ability ifadministered with sufficient frequency and concentration. The classicdefinition of factor VIII, in fact, is that substance present in normalblood plasma that corrects the clotting defect in plasma derived fromindividuals with hemophilia A.

The development of antibodies (“inhibitors” or “inhibitory antibodies”)that inhibit the activity of factor VIII is a serious complication inthe management of patients with hemophilia. Autoantibodies develop inapproximately 20% of patients with hemophilia A in response totherapeutic infusions of factor VIII. In previously untreated patientswith hemophilia A who develop inhibitors, the inhibitor usually developswithin one year of treatment. Additionally, autoantibodies thatinactivate factor VIII occasionally develop in individuals withpreviously normal factor VIII levels. If the inhibitor titer is lowenough, patients can be managed by increasing the dose of factor VIII.However, often the inhibitor titer is so high that it cannot beoverwhelmed by factor VIII. An alternative strategy is to bypass theneed for factor VIII during normal hemostasis using factor IX complexpreparations (for example, KONYNE®, Proplex®) or recombinant humanfactor VIIIa. Additionally, since porcine factor VIII usually hassubstantially less reactivity with inhibitors than human factor VIII, apartially purified porcine factor VIII preparation (HYATE:C®) is used.Many patients who have developed inhibitory antibodies to human factorVIII have been successfully treated with porcine factor VIII and havetolerated such treatment for long periods of time. However,administration of porcine factor VIII is not a complete solution becauseinhibitors may develop to porcine factor VIII after one or moreinfusions.

Several preparations of human plasma-derived factor VIII of varyingdegrees of purity are available commercially for the treatment ofhemophilia A. These include a partially-purified factor VIII derivedfrom the pooled blood of many donors that is heat- and detergent-treatedfor viruses but contain a significant level of antigenic proteins; amonoclonal antibody-purified factor VIII that has lower levels ofantigenic impurities and viral contamination; and recombinant humanfactor VIII, clinical trials for which are underway. Unfortunately,human factor VIII is unstable at physiologic concentrations and pH, ispresent in blood at an extremely low concentration (0.2 μg/ml plasma),and has low specific clotting activity.

Hemophiliacs require daily replacement of factor VIII to preventbleeding and the resulting deforming hemophilic arthropathy. However,supplies have been inadequate and problems in therapeutic use occur dueto difficulty in isolation and purification, immunogenicity, and thenecessity of removing the AIDS and hepatitis infectivity risk. The useof recombinant human factor VIII or partially-purified porcine factorVIII will not resolve all the problems.

The problems associated with the commonly used, commercially available,plasma-derived factor VIII have stimulated significant interest in thedevelopment of a better factor VIII product. There is a need for a morepotent factor VIII molecule so that more units of clotting activity canbe delivered per molecule; a factor VIII molecule that is stable at aselected pH and physiologic concentration; a factor VIII molecule thatis less apt to cause production of inhibitory antibodies; and a factorVIII molecule that evades immune detection in patients who have alreadyacquired antibodies to human factor VIII.

It is therefore an object of the present invention to provide a factorVIII that corrects hemophilia in a patient deficient in factor VIII orhaving inhibitors to factor VIII.

It is a further object of the present invention to provide methods fortreatment of hemophiliacs.

It is still another object of the present invention to provide a factorVIII that is stable at a selected pH and physiologic concentration.

It is yet another object of the present invention to provide a factorVIII that has greater coagulant activity than human factor VIII.

It is an additional object of the present invention to provide a factorVIII against which less antibody is produced.

SUMMARY OF THE INVENTION

The present invention provides isolated, purified, hybrid factor VIIImolecules and fragments thereof with coagulant activity including hybridfactor VIII having factor VIII amino acid sequence derived from humanand pig or other non-human mammal (together referred to herein as“animal”); or in a second embodiment including a hybrid equivalentfactor VIII having factor VIII amino acid sequence derived from human oranimal or both and amino acid sequence having no known sequence identityto factor VIII (“non-factor VIII amino acid sequence”), preferablysubstituted in an antigenic and/or immunogenic region of the factorVIII, is described. One skilled in the art will realize that numeroushybrid factor VIII constructs can be prepared including, but not limitedto, human/animal factor VIII having greater coagulant activity thanhuman factor VIII (“superior coagulant activity”); non-immunogenichuman/equivalent factor VIII; non-antigenic human/equivalent orhuman/animal factor VIII; non-immunogenic human/animal orhuman/equivalent factor VIII having superior coagulant activity;non-antigenic human/animal or human/animal/equivalent factor VIII havingsuperior coagulant activity; non-immunogenic, non-antigenichuman/equivalent or human/equivalent/animal factor VIII; andnon-immunogenic, non-antigenic human/animal/equivalent factor VIIIhaving superior coagulant activity.

The hybrid factor VIII molecule is produced by isolation andrecombination of human and animal factor VIII subunits or domains; or bygenetic engineering of the human and animal factor VIII genes.

In a preferred embodiment, recombinant DNA methods are used tosubstitute elements of animal factor VIII for the corresponding elementsof human factor VIII, resulting in hybrid human/animal factor VIIImolecules. In a second preferred embodiment, recombinant DNA methods areused to replace one or more amino acids in the human or animal factorVIII or in a hybrid human/animal factor VIII with amino acids that haveno known sequence identity to factor VIII, preferably a sequence ofamino acids that has less immunoreactivity with naturally occurringinhibitory antibodies to factor VIII (“nonantigenic amino acidsequence”) and/or is less apt to elicit the production of antibodies tofactor VIII (“non-immunogenic amino acid sequence”) than human factorVIII. An example of an amino acid sequence that can be used to replaceimmunogenic or antigenic sequence is a sequence of alanine residues.

In another embodiment, subunits of factor VIII are isolated and purifiedfrom human or animal plasma, and hybrid human/animal factor VIII isproduced either by mixture of animal heavy chain subunits with humanlight chain subunits or by mixture of human heavy chain subunits withanimal light chain subunits, thereby producing human light chain/animalheavy chain and human heavy chain/animal light chain hybrid molecules.These hybrid molecules are isolated by ion exchange chromatography.

Alternatively, one or more domains or partial domains of factor VIII areisolated and purified from human or animal plasma, and hybridhuman/animal factor VIII is produced by mixture of domains or partialdomains from one species with domains or partial domains of the secondspecies. Hybrid molecules can be isolated by ion exchangechromatography.

Methods for preparing highly purified hybrid factor VIII are describedhaving the steps of: (a) isolation of subunits of plasma-derived humanfactor VIII and subunits of plasma-derived animal factor VIII, followedby reconstitution of coagulant activity by mixture of human and animalsubunits, followed by isolation of hybrid human/animal factor VIII byion exchange chromatography; (b) isolation of domains or partial domainsof plasma-derived human factor VIII and domains or partial domains ofplasma-derived animal factor VIII, followed by reconstitution ofcoagulant activity by mixture of human and animal domains, followed byisolation of hybrid human/animal factor VIII by ion exchangechromatography; (c) construction of domains or partial domains of animalfactor VIII by recombinant DNA technology, and recombinant exchange ofdomains of animal and human factor VIII to produce hybrid human/animalfactor VIII with coagulant activity; (d) creation of hybrid human/animalfactor VIII by replacement of specific amino acid residues of the factorVIII of one species with the corresponding unique amino acid residues ofthe factor VIII of the other species; or (e) creation of a hybridequivalent factor VIII molecule having human or animal amino acidsequence or both, in which specific amino acid residues of the factorVIII are replaced with amino acid residues having no known sequenceidentity to factor VIII by site-directed mutagenesis.

The determination of the entire DNA sequence encoding porcine factorVIII set forth herein has enabled, for the first time, the synthesis offull-length porcine factor VIII by expressing the DNA encoding porcinefactor VIII in a suitable host cell. Purified recombinant porcine factorVIII is therefore an aspect of the present invention. The DNA encodingeach domain of porcine factor VIII as well as any specified fragmentthereof, can be similarly expressed, either by itself or in combinationwith DNA encoding human factor VIII to make the hybrid human/porcine,factor VIII described herein. Furthermore, porcine fVIII having all orpart of the B domain deleted (B-domainless porcine fVIII) is madeavailable as part of the present invention, by expression DNA encodingporcine fVIII having a deletion of one or more codons of the B-domain.

Some embodiments of hybrid or hybrid equivalent factor VIII havespecific activity greater than that of human factor VIII and equal to orgreater than that of porcine factor VIII. Some embodiments of hybrid orhybrid equivalent factor VIII have equal or less immunoreactivity withinhibitory antibodies to factor VIII and/or less immunogenicity inhumans or animals, compared to human or porcine factor VIII.

Also provided are pharmaceutical compositions and methods for treatingpatients having factor VIII deficiency comprising administering thehybrid or hybrid equivalent factor VIII.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A–1H taken together provide an aligned sequence comparison of thehuman (SEQ ID NO:2), pig (SEQ ID NO:37) and mouse (SEQ ID NO:6) factorVIII amino acid sequences.

DETAILED DESCRIPTION OF THE INVENTION

Unless otherwise specified or indicated, as used herein, “factor VIII”denotes any functional factor VIII protein molecule from any animal, anyhybrid factor VIII or modified factor VIII, “hybrid factor VIII” or“hybrid protein” denotes any functional factor VIII protein molecule orfragment thereof comprising factor VIII amino acid sequence from human,porcine, and/or non-human, non-porcine mammalian species. Suchcombinations include, but are not limited to, any or all of thefollowing hybrid factor VIII molecules or fragments thereof: (1)human/porcine; (2) human/non-human, non-porcine mammalian, such ashuman/mouse; (3) porcine/non-human, non-porcine mammalian, such asmouse/dog. Such combinations also include hybrid factor VIII equivalentmolecules or fragments thereof, as further defined below, comprisingfactor VIII amino acid sequence of hybrid, human, porcine, or non-human,non-porcine mammalian origin in which amino acid sequence having noknown sequence identity to factor VIII is substituted. Such hybridcombinations also include hybrid factor VIII amino sequence derived frommore than two species, such as human/pig/mouse, or from two or morespecies in which amino acid sequence having no known sequence identityto factor VIII is substituted. Unless otherwise indicated, “hybridfactor VIII” includes fragments of the hybrid factor VIII, which can beused, as described below in one exemplary embodiment, as probes forresearch purposes or as diagnostic reagents.

As used herein, “mammalian factor VIII” includes factor VIII with aminoacid sequence derived from any non-human mammal, unless otherwisespecified. “Animal”, as used herein, refers to pig and other non-humanmammals.

A “fusion protein” or “fusion factor VIII or fragment thereof”, as usedherein, is the product of a hybrid gene in which the coding sequence forone protein is extensively altered, for example, by fusing part of it tothe coding sequence for a second protein from a different gene toproduce a hybrid gene that encodes the fusion protein. As used herein, afusion protein is a subset of the hybrid factor VIII protein describedin this application.

A “corresponding” nucleic acid or amino acid or sequence of either, asused herein, is one present at a site in a factor VIII or hybrid factorVIII molecule or fragment thereof that has the same structure and/orfunction as a site in the factor VIII molecule of another species,although the nucleic acid or amino acid number may not be identical. Asequence “corresponding to” another factor VIII sequence substantiallycorresponds to such sequence, and hybridizes to the sequence of thedesignated SEQ ID NO. under stringent conditions. A sequence“corresponding to” another factor VIII sequence also includes a sequencethat results in the expression of a factor VIII or claimed procoagulanthybrid factor VIII or fragment thereof and would hybridize to thedesignated SEQ ID NO. but for the redundancy of the genetic code.

A “unique” amino acid residue or sequence, as used herein, refers to anamino acid sequence or residue in the factor VIII molecule of onespecies that is different from the homologous residue or sequence in thefactor VIII molecule of another species. “Specific activity,” as usedherein, refers to the activity that will correct the coagulation defectof human factor VIII deficient plasma. Specific activity is measured inunits of clotting activity per milligram total factor VIII protein in astandard assay in which the clotting time of human factor VIII deficientplasma is compared to that of normal human plasma. One unit of factorVIII activity is the activity present in one milliliter of normal humanplasma. In the assay, the shorter the time for clot formation, thegreater the activity of the factor VIII being assayed. Hybridhuman/porcine factor VIII has coagulation activity in a human factorVIII assay. This activity, as well as that of other hybrid or hybridequivalent factor VIII molecules or fragments thereof, may be less than,equal to, or greater than that of either plasma-derived or recombinanthuman factor VIII.

The human factor VIII DNA nucleotide and predicted amino acid sequencesare shown in SEQ ID NOs:1 and 2, respectively. Factor VIII issynthesized as an approximately 300 kDa single chain protein withinternal sequence homology that defines the “domain” sequenceNH₂-A1–A2-B-A3-CI-C2-COOH. In a factor VIII molecule, a “domain”, asused herein, is a continuous sequence of amino acids that is defined byinternal amino acid sequence identity and sites of proteolytic cleavageby thrombin. Unless otherwise specified, factor VIII domains include thefollowing amino acid residues, when the sequences are aligned with thehuman amino acid sequence (SEQ ID NO:2): A1, residues Ala1-Arg372; A2,residues Ser373-Arg740; B, residues Ser741-Arg1648; A3, residuesSer1690-IIe2032; C1, residues Arg2033-Asn2172; C2, residuesSer2173-Tyr2332. The A3-C1–C2 sequence includes residuesSer1690-Tyr2332. The remaining sequence, residues Glu1649-Arg1689, isusually referred to as the factor VIII light chain activation peptide.Factor VIII is proteolytically activated by thrombin or factor Xa, whichdissociates it from von Willebrand factor, forming factor VIIIa, whichhas procoagulant function. The biological function of factor VIIIa is toincrease the catalytic efficiency of factor IXa toward factor Xactivation by several orders of magnitude. Thrombin-activated factorVIIIa is a 160 kDa A1/A2/A3-C1–C2 heterotrimer that forms a complex withfactor IXa and factor X on the surface of platelets or monocytes. A“partial domain” as used herein is a continuous sequence of amino acidsforming part of a domain.

“Subunits” of human or animal factor VIII, as used herein, are the heavyand light chains of the protein. The heavy chain of factor VIII containsthree domains, A1, A2, and B. The light chain of factor VIII alsocontains three domains, A3, C1, and C2.

The hybrid factor VIII or fragment thereof can be made (1) bysubstitution of isolated, plasma-derived animal subunits or humansubunits (heavy or light chains) for corresponding human subunits oranimal subunits; (2) by substitution of human domains or animal domains(A1, A2, A3, B, C1, and C2) for corresponding animal domains or humandomains; (3) by substitution of parts of human domains or animal domainsfor parts of animal domains or human domains; (4) by substitution of atleast one specific sequence including one or more unique human or animalamino acid(s) for the corresponding animal or human amino acid(s); or(5) by substitution of amino acid sequence that has no known sequenceidentity to factor VIII for at least one sequence including one or morespecific amino acid residue(s) in human, animal, or hybrid factor VIIIor fragments thereof. A “B-domainless” hybrid factor VIII, hybridequivalent factor VIII, or fragment of either, as used herein, refers toany one of the hybrid factor VIII constructs described herein that lacksthe B domain.

The terms “epitope”, “antigenic site”, and “antigenic determinant”, asused herein, are used synonymously and are defined as a portion of thehuman, animal, hybrid, or hybrid equivalent factor VIII or fragmentthereof that is specifically recognized by an antibody. It can consistof any number of amino acid residues, and it can be dependent upon theprimary, secondary, or tertiary structure of the protein. In accordancewith this disclosure, a hybrid factor VIII, hybrid factor VIIIequivalent, or fragment of either that includes at least one epitope maybe used as a reagent in the diagnostic assays described below. In someembodiments, the hybrid or hybrid equivalent factor VIII or fragmentthereof is not cross-reactive or is less cross-reactive with allnaturally occurring inhibitory factor VIII antibodies than human orporcine factor VIII.

The term “immunogenic site”, as used herein, is defined as a region ofthe human or animal factor VIII, hybrid or hybrid equivalent factorVIII, or fragment thereof that specifically elicits the production ofantibody to the factor VIII, hybrid, hybrid equivalent, or fragment in ahuman or animal, as measured by routine protocols, such as immunoassay,e.g. ELISA, or the Bethesda assay, described herein. It can consist ofany number of amino acid residues, and it can be dependent upon theprimary, secondary, or tertiary structure of the protein. In someembodiments, the hybrid or hybrid equivalent factor VIII or fragmentthereof is nonimmunogenic or less immunogenic in an animal or human thanhuman or porcine factor VIII.

As used herein, a “hybrid factor VIII equivalent molecule or fragmentthereof” or “hybrid equivalent factor VIII or fragment thereof” is anactive factor VIII or hybrid factor VIII molecule or fragment thereofcomprising at least one sequence including one or more amino acidresidues that have no known identity to human or animal factor VIIIsequence substituted for at least one sequence including one or morespecific amino acid residues in the human, animal, or hybrid factor VIIIor fragment thereof. The sequence of one or more amino acid residuesthat have no known identity to human or animal factor VIII sequence isalso referred to herein as “non-factor VIII amino acid sequence”. In apreferred embodiment, the amino acid(s) having no known sequenceidentity to factor VIII sequence are alanine residues. In anotherpreferred embodiment, the specific factor VIII sequence for which theamino acid(s) having no known sequence identity to factor VIII sequenceare substituted includes an antigenic site that is immunoreactive withnaturally occurring factor VIII inhibitory antibodies, such that theresulting hybrid factor VIII equivalent molecule or fragment thereof isless immunoreactive or not immunoreactive with factor VIII inhibitoryantibodies. In yet another preferred embodiment, the specific hybridfactor VIII sequence for which the amino acid(s) having no knownsequence identity to factor VIII sequence are substituted includes animmunogenic site that elicits the formation of factor VIII inhibitoryantibodies in an animal or human, such that the resulting hybrid factorVIII equivalent molecule or fragment thereof is less immunogenic.

“Factor VIII deficiency,” as used herein, includes deficiency inclotting activity caused by production of defective factor VIII, byinadequate or no production of factor VIII, or by partial or totalinhibition of factor VIII by inhibitors. Hemophilia A is a type offactor VIII deficiency resulting from a defect in an X-linked gene andthe absence or deficiency of the factor VIII protein it encodes.

As used herein, “diagnostic assays” include assays that in some mannerutilize the antigen-antibody interaction to detect and/or quantify theamount of a particular antibody that is present in a test sample toassist in the selection of medical therapies. There are many such assaysknown to those of skill in the art. As used herein, however, the hybridor hybrid equivalent factor VIII DNA or fragment thereof and proteinexpressed therefrom, in whole or in part, can be substituted for thecorresponding reagents in the otherwise known assays, whereby themodified assays may be used to detect and/or quantify antibodies tofactor VIII. It is the use of these reagents, the hybrid or hybridequivalent factor VIII DNA or fragment thereof or protein expressedtherefrom, that permits modification of known assays for detection ofantibodies to human or animal factor VIII or to hybrid human/animalfactor VIII. Such assays include, but are not limited to ELISAs,immunodiffusion assays, and immunoblots. Suitable methods for practicingany of these assays are known to those of skill in the art. As usedherein, the hybrid or hybrid equivalent factor VIII or fragment thereofthat includes at least one epitope of the protein can be used as thediagnostic reagent. Examples of other assays in which the hybrid orhybrid equivalent factor VIII or fragment thereof can be used includethe Bethesda assay and anticoagulation assays.

General Description of Methods

U.S. Ser. No. 07/864,004 described the discovery of hybrid human/porcinefactor VIII molecules having coagulant activity, in which elements ofthe factor VIII molecule of human or pig are substituted forcorresponding elements of the factor VIII molecule of the other species.U.S. Ser. No. 08/212,133 and PCT/US94/13200 describe procoagulant hybridhuman/animal and hybrid equivalent factor VIII molecules, in whichelements of the factor VIII molecule of one species are substituted forcorresponding elements of the factor VIII molecule of the other species.

The present invention provides hybrid human/animal, animal/animal, andequivalent factor VIII molecules and fragments thereof, and the nucleicacid sequences encoding such hybrids, some of which have greatercoagulant activity in a standard clotting assay when compared tohighly-purified human factor VIII; and/or are less immunoreactive toinhibitory antibodies to human or porcine factor VIII than human orporcine factor VIII; and/or are less immunogenic in a human or animalthan human or porcine factor VIII. These hybrid factor VIII moleculescan be constructed as follows.

At least five types of active hybrid human/porcine or hybrid equivalentfactor VIII molecules or fragments thereof, the nucleic acid sequencesencoding these hybrid factor VIII molecules, and the methods forpreparing them are disclosed herein: those obtained (1) by substitutinga human or porcine subunit (i.e., heavy chain or light chain) for thecorresponding porcine or human subunit; (2) by substituting one or morehuman or porcine domain(s) (i.e., A1, A2, A3, B, C1, and C2) for thecorresponding porcine or human domain(s); (3) by substituting acontinuous part of one or more human or porcine domain(s) for thecorresponding part of one or more porcine or human domain(s); (4) bysubstituting at least one specific sequence including one or more uniqueamino acid residue(s) in human or porcine factor VIII for thecorresponding porcine or human sequence; and (5) by substituting atleast one sequence including one or more amino acid residue(s) having noknown sequence identity to factor VIII (“non-factor VIII amino acidsequence”) for at least one specific sequence of one or more amino acidsin human, porcine, or hybrid human/porcine factor VIII.

At least five types of active hybrid human/non-human, non-porcinemammalian or hybrid equivalent factor VIII molecules or fragmentsthereof, and the nucleic acid sequences encoding them, can also beprepared by the same methods: those obtained (1) by substituting a humanor non-human, non-porcine mammalian subunit (i.e., heavy chain or lightchain) for the corresponding non-human, non-porcine mammalian or humansubunit; (2) by substituting one or more human or non-human, non-porcinemammalian domain(s) (i.e., A1, A2, A3, B, C1 and C2) for thecorresponding non-human, non-porcine mammalian or human domain(s); (3)by substituting a continuous part of one or more human or non-human,non-porcine mammalian domain(s) for the corresponding part of one ormore non-human, non-porcine mammalian or human domain(s); (4) bysubstituting at least one specific sequence including one or more uniqueamino acid residue(s) in human or non-human, non-porcine mammalianfactor VIII for the corresponding non-human, non-porcine mammalian orhuman sequence; and (5) by substituting at least one sequence includingone or more amino acid residue(s) having no known sequence identity tofactor VIII (“non-factor VIII amino acid sequence”) for at least onespecific sequence of one or more amino acids in human, non-human,non-porcine mammalian, or hybrid human/non-human, non-porcine mammalianfactor VIII.

Further, one skilled in the art will readily recognize that the samemethods can be used to prepare at least five types of active hybridfactor VIII molecules or fragments thereof, corresponding to types(1)–(5) in the previous two paragraphs, comprising factor VIII aminoacid sequence from two or more non-human mammals, such as porcine/mouse,and further comprising non-factor VIII amino acid sequence.

Hybrid human/animal, animal/animal, and equivalent factor VIII proteinsor fragments thereof listed above under groups (1)–(3) are made byisolation of subunits, domains, or continuous parts of domains ofplasma-derived factor VIII, followed by reconstitution and purification.Hybrid human/animal, animal/animal, and equivalent factor VIII proteinsor fragments thereof described under groups (3)–(5) above are made byrecombinant DNA methods. The hybrid molecule may contain a greater orlesser percentage of human than animal sequence, depending on the originof the various regions, as described in more detail below.

Since current information indicates that the B domain has no inhibitoryepitope and has no known effect on factor VIII function, in someembodiments the B domain is deleted in the active hybrid or hybridequivalent factor VIII molecules or fragments thereof (“B(−) factorVIII”) prepared by any of the methods described herein.

It is shown in Example 4 that hybrid human/porcine factor VIIIcomprising porcine heavy chain and human light chain and correspondingto the first type of hybrid listed above has greater specific coagulantactivity in a standard clotting assay compared to human factor VIII. Thehybrid human/animal or equivalent factor VIII with coagulant activity,whether the activity is higher, equal to, or lower than that of humanfactor VIII, can be useful in treating patients with inhibitors, sincethese inhibitors can react less with hybrid human/animal or equivalentfactor VIII than with either human or porcine factor VIII.

Preparation of Hybrid Factor VIII Molecules from Isolated Human andAnimal Factor VIII Subunits by Reconstitution:

The present invention provides hybrid human/animal factor VIII moleculesor fragments thereof, with subunit substitutions, the nucleic acidsequences encoding these hybrids, methods for preparing and isolatingthem, and methods for characterizing their procoagulant activity. Onemethod, modified from procedures reported by Fay, P. J. et al. (1990) J.Biol. Chem. 265:6197; and Lollar, J. S. et al. (1988) J. Biol. Chem.263:10451, involves the isolation of subunits (heavy and light chains)of human and animal factor VIII, followed by recombination of humanheavy chain and animal light chain or by recombination of human lightchain and animal heavy chain.

Isolation of both human and animal individual subunits involvesdissociation of the light chain/heavy chain dimer. This is accomplished,for example, by chelation of calcium with ethylenediaminetetraaceticacid (EDTA), followed by monoS™ HPLC (Pharmacia-LKB, Piscataway, N.J.).Hybrid human/animal factor VIII molecules are reconstituted fromisolated subunits in the presence of calcium. Hybrid human lightchain/animal heavy chain or animal light chain/human heavy chain factorVIII is isolated from unreacted heavy chains by monoS™ HPLC byprocedures for the isolation of porcine factor VIII, such as describedby Lollar, J. S. et al. (1988) Blood 71:137–143.

These methods, used in one embodiment to prepare active hybridhuman/porcine factor VIII, described in detail in the examples below,result in hybrid human light chain/porcine heavy chain molecules withgreater than six times the procoagulant activity of human factor VIII.

Other hybrid human/non-human, non-porcine mammalian factor VIIImolecules can be prepared, isolated, and characterized for activity bythe same methods. One skilled in the art will readily recognize thatthese methods can also be used to prepare, isolate, and characterize foractivity hybrid animal/animal factor VIII, such as porcine/mouse,comprising the light or heavy chain or one species is combined with theheavy or light chain of the other species.

Preparation of Hybrid Factor VIII Molecules from Isolated Human andAnimal Factor VIII Domains by Reconstitution:

The present invention provides hybrid human/animal factor VIII moleculesor fragments thereof with domain substitutions, the nucleic acidsequences encoding them, methods for preparing and isolating them, andmethods for characterizing their procoagulant activity. One methodinvolves the isolation of one or more domains of human and one or moredomains of animal factor VIII, followed by recombination of human andanimal domains to form hybrid human/animal factor VIII with coagulantactivity, as described by Lollar, P. et al. (Nov. 25, 1992) J. Biol.Chem. 267(33):23652–23657, for hybrid human/porcine factor VIII.

Specifically provided is a hybrid human/porcine factor VIII withsubstitution of the porcine A2 domain for the human A2 domain, whichembodiment illustrates a method by which domain-substituted hybridhuman/non-human, non-porcine mammalian factor VIII can be constructed.Plasma-derived non-human, non-porcine mammalian and human A1/A3-C1–C2dimers are isolated by dissociation of the A2 domain from factor VIIIa.This is accomplished, for example, in the presence of NaOH, after whichthe mixture is diluted and the dimer is eluted using monoS™ HPLC(Pharmacia-LKB, Piscataway, N.J.). The A2 domain is isolated from factorVIIIa as a minor component in the monoS™ HPLC. Hybrid human/animalfactor VIII molecules are reconstituted by mixing equal volumes of theA2 domain of one species and the A1/A3-C1–C2 dimer of the other species.

Hybrid human/animal factor VIII or fragments thereof with one or moredomain substitutions is isolated from the mixture of unreacted dimersand A2 by monoS™ HPLC by procedures for the isolation of porcine factorVIII, as described by Lollar, J. S. et al. (1988) Blood 71:137–143.Routine methods can also be used to prepare and isolate the A1, A3, C1,C2, and B domains of the factor VIII of one species, any one or more ofwhich can be substituted for the corresponding domain in the factor VIIIof the other species. One skilled in the art will readily recognize thatthese methods can also be used to prepare, isolate, and characterize foractivity domain-substituted hybrid animal/animal factor VIII, such asporcine/mouse.

These methods, described in detail in the examples below, result inhybrid factor VIII molecules with procoagulant activity.

Preparation of Hybrid Factor VIII Molecules by Recombinant Engineeringof the Sequences Encoding Human, Animal, and Hybrid Factor VIIISubunits, Domains, or Parts of Domains:

Substitution of Subunits, Domains, Continuous Parts of Domains:

The present invention provides active, recombinant hybrid human/animaland hybrid equivalent factor VIII molecules and fragments thereof withsubunit, domain, and amino acid sequence substitutions, the nucleic acidsequences encoding these hybrids, methods for preparing and isolatingthem, and methods for characterizing their coagulant, immunoreactive,and immunogenic properties.

The human factor VIII gene was isolated and expressed in mammaliancells, as reported by Toole, J. J. et al. (1984) Nature 312:342–347(Genetics Institute); Gitschier, J. et al.(1984) Nature 312:326–330(Genentech); Wood, W. I. et al. (1984) Nature 312:330–337 (Genentech);Vehar, G. A. et al. (1984) Nature 312:337–342 (Genentech); WO 87/04187;WO 88/08035; WO 88/03558; U.S. Pat. No. 4,757,006, and the amino acidsequence was deduced from cDNA. U.S. Pat. No. 4,965,199 to Capon et al.discloses a recombinant DNA method for producing factor VIII inmammalian host cells and purification of human factor VIII. Human factorVIII expression on CHO (Chinese hamster ovary) cells and BHKC (babyhamster kidney cells) has been reported. Human factor VIII has beenmodified to delete part or all of the B domain (U.S. Pat. No.4,868,112), and replacement of the human factor VIII B domain with thehuman factor V B domain has been attempted (U.S. Pat. No. 5,004,803).The cDNA sequence encoding human factor VIII and predicted amino acidsequence are shown in SEQ ID NOs:1 and 2, respectively.

Porcine factor VIII has been isolated and purified from plasma [Fass, D.N. et al. (1982) Blood 59:594]. Partial amino acid sequence of porcinefactor VIII corresponding to portions of the N-terminal light chainsequence having homology to ceruloplasmin and coagulation factor V andlargely incorrectly located were described by Church et al. (1984) Proc.Natl. Acad. Sci. USA 81:6934. Toole, J. J. et al. (1984) Nature312:342–347 described the partial sequencing of the N-terminal end offour amino acid fragments of porcine factor VIII but did notcharacterize the fragments as to their positions in the factor VIIImolecule. The amino acid sequence of the B and part of the A2 domains ofporcine factor VIII were reported by Toole, J. J. et al. (1986) Proc.Natl. Acad. Sci, USA 83:5939–5942. The cDNA sequence encoding thecomplete A2 domain of porcine factor VIII and predicted amino acidsequence and hybrid human/porcine factor VIII having substitutions ofall domains, all subunits, and specific amino acid sequences weredisclosed in U.S. Ser. No. 07/864,004 entitled “Hybrid Human/Porcinefactor VIII ” filed Apr. 7, 1992 by John S. Lollar and Marschall S.Runge, which issued as U.S. Pat. No. 5,364,771 on Nov. 15, 1994, and inWO 93/20093. The cDNA sequence encoding the A2 domain of porcine factorVIII having sequence identity to residues 373–740 in mature human factorVIII, as shown in SEQ ID NO:1, and the predicted amino acid sequence areshown in SEQ ID NOs:3 and 4, respectively. More recently, the nucleotideand corresponding amino acid sequences of the A1 and A2 domains ofporcine factor VIII and a chimeric factor VIII with porcine A1 and/or A2domains substituted for the corresponding human domains were reported inWO 94/11503.

Both porcine and human factor VIII are isolated from plasma as a twosubunit protein. The subunits, known as the heavy chain and light chain,are held together by a non-covalent bond that requires calcium or otherdivalent metal ions. The heavy chain of factor VIII contains threedomains, A1, A2, and B, which are linked covalently. The light chain offactor VIII also contains three domains, designated A3, C1, and C2. TheB domain has no known biological function and can be removed from themolecule proteolytically or by recombinant DNA technology methodswithout significant alteration in any measurable parameter of factorVIII. Human recombinant factor VIII has a similar structure and functionto plasma-derived factor VIII, though it is not glycosylated unlessexpressed in mammalian cells.

Both human and porcine activated factor VIII (“factor VIIIa”) have threesubunits due to cleavage of the heavy chain between the A1 and A2domains. This structure is designated A1/A2/A3-C1–C2. Human factor VIIIais not stable under the conditions that stabilize porcine factor VIIIa,presumably because of the weaker association of the A2 subunit of humanfactor VIIIa. Dissociation of the A2 subunit of human and porcine factorVIIIa is associated with loss of activity in the factor VIIIa molecule.

Using as probes the known sequence of parts of the porcine factor VIIImolecule, the domains of the porcine factor VIII molecule that have notbeen sequenced to date can be sequenced by standard, established cloningtechniques, such as those described in Weis, J. H., “Construction ofrecombinant DNA libraries,” in Current Protocols in Molecular Biology,F. M. Ausubel et al., eds. (1991); and Sambrook, J., et al., MolecularCloning, A Laboratory Manual, so that full length hybrids can beconstructed.

Specifically provided as an exemplary and a preferred embodiment isactive recombinant hybrid human/porcine factor VIII having substitutedA2 domain, the nucleic acid sequence encoding it, and the methods forpreparing, isolating, and characterizing its activity. The methods bywhich this hybrid construct is prepared can also be used to prepareactive recombinant hybrid human/porcine factor VIII or fragments thereofhaving substitution of subunits, continuous parts of domains, or domainsother than A2. One skilled in the art will recognize that these methodsalso demonstrate how other recombinant hybrid human/non-human,non-porcine mammalian or animal/animal hybrid factor VIII molecules orfragments thereof can be prepared in which subunits, domains, orcontinuous parts of domains are substituted.

Recombinant hybrid human/porcine factor VIII is prepared starting withhuman cDNA (Biogen, Inc.) or porcine cDNA (described herein) encodingthe relevant factor VIII sequence. In a preferred embodiment, the factorVIII encoded by the cDNA includes domains A1–A2-A3-C1–C2, lacking theentire B domain, and corresponds to amino acid residues 1–740 and1649–2332 of single chain human factor VIII (see SEQ ID NO:2), accordingto the numbering system of Wood et al. (1984) Nature 312:330–337.

Individual subunits, domains, or continuous parts of domains of porcineor human factor VIII cDNA can be and have been cloned and substitutedfor the corresponding human or porcine subunits, domains, or parts ofdomains by established mutagenesis techniques. For example, Lubin, I. M.et al. (1994) J. Biol. Chem. 269(12):8639–8641 describes techniques forsubstituting the porcine A2 domain for the human domain using convenientrestriction sites. Other methods for substituting any arbitrary regionof the factor VIII cDNA of one species for the factor VIII cDNA ofanother species include splicing by overlap extension (“SOE”), asdescribed by Horton, R. M. et al. (1993) Meth. Enzymol 217:270–279.

The hybrid factor VIII cDNA encoding subunits, domains, or parts ofdomains or the entire hybrid cDNA molecules are cloned into expressionvectors for ultimate expression of active hybrid human/porcine factorVIII protein molecules in cultured cells by established techniques, asdescribed by Selden, R. F., “Introduction of DNA into mammalian cells,”in Current Protocols in Molecular Biology, F. M. Ausubel et al., eds(1991).

In a preferred embodiment, a hybrid human/porcine cDNA encoding factorVIII, in which the porcine sequence encodes a domain or part domain,such as the A2 domain or part domain, is inserted in a mammalianexpression vector, such as ReNeo, to form a hybrid factor VIIIconstruct. Preliminary characterization of the hybrid factor VIII isaccomplished by insertion of the hybrid cDNA into the ReNeo mammalianexpression vector and transient expression of the hybrid protein inCOS-7 cells. A determination of whether active hybrid protein isexpressed can then be made. The expression vector construct is usedfurther to stably transfect cells in culture, such as baby hamsterkidney cells, using methods that are routine in the art, such asliposome-mediated transfection (Lipofectin™, Life Technologies, Inc.).Expression of recombinant hybrid factor VIII protein can be confirmed,for example, by sequencing, Northern and Western blotting, or polymerasechain reaction (PCR). Hybrid factor VIII protein in the culture media inwhich the transfected cells stably expressing the protein are maintainedcan be precipitated, pelleted, washed, and resuspended in an appropriatebuffer, and the recombinant hybrid factor VIII protein purified bystandard techniques, including immunoaffinity chromatography using, forexample, monoclonal anti-A2-Sepharose™.

In a further embodiment, the hybrid factor VIII comprising subunit,domain, or amino acid sequence substitutions is expressed as a fusionprotein from a recombinant molecule in which sequence encoding a proteinor peptide that enhances, for example, stability, secretion, detection,isolation, or the like is inserted in place adjacent to the factor VIIIencoding sequence. Established protocols for use of homologous orheterologous species expression control sequences including, forexample, promoters, operators, and regulators, in the preparation offusion proteins are known and routinely used in the art. See CurrentProtocols in Molecular Biology (Ausubel, F. M., et al., eds), WileyInterscience, N.Y.

The purified hybrid factor VIII or fragment thereof can be assayed forimmunoreactivity and coagulation activity by standard assays including,for example, the plasma-free factor VIII assay, the one-stage clottingassay, and the enzyme-linked immunosorbent assay using purifiedrecombinant human factor VIII as a standard.

Other vectors, including both plasmid and eukaryotic viral vectors, maybe used to express a recombinant gene construct in eukaryotic cellsdepending on the preference and judgment of the skilled practitioner(see, for example, Sambrook et al., Chapter 16). Other vectors andexpression systems, including bacterial, yeast, and insect cell systems,can be used but are not preferred due to differences in, or lack of,glycosylation.

Recombinant hybrid factor VIII protein can be expressed in a variety ofcells commonly used for culture and recombinant mammalian proteinexpression. In particular, a number of rodent cell lines have been foundto be especially useful hosts for expression of large proteins.Preferred cell lines, available from the American Type CultureCollection, Rockville, Md., include baby hamster kidney cells, andchinese hamster ovary (CHO) cells which are cultured using routineprocedures and media.

The same methods employed for preparing hybrid human/porcine factor VIIIhaving subunit, domain, or amino acid sequence substitution can be usedto prepare other recombinant hybrid factor VIII protein and fragmentsthereof and the nucleic acid sequences encoding these hybrids, such ashuman/non-human, non-porcine mammalian or animal/animal. Starting withprimers from the known human DNA sequence, the murine and part of theporcine factor VIII cDNA have been cloned. Factor VIII sequences ofother species for use in preparing a hybrid human/animal oranimal/animal factor VIII molecule can be obtained using the known humanand porcine DNA sequences as a starting point. Other techniques that canbe employed include PCR amplification methods with animal tissue DNA,and use of a cDNA library from the animal to clone out the factor VIIIsequence.

As an exemplary embodiment, hybrid human/mouse factor VIII protein canbe made as follows. DNA clones corresponding to the mouse homolog of thehuman factor VIII gene have been isolated and sequenced and the aminoacid sequence of mouse factor VIII protein predicted, as described inElder, G., et al. (1993) Genomics 16(2):374–379, which also includes acomparison of the predicted amino acid sequences of mouse, human, andpart of porcine factor VIII molecules. The mouse factor VIII cDNAsequence and predicted amino acid sequence are shown in SEQ ID NO:5 andSEQ ID NO:8, respectively. In a preferred embodiment, the RNAamplification with transcript sequencing (RAWTS) methods described inSarkar, G. et al. (1989) Science 244:331–334, can be used. Briefly, thesteps are (1) cDNA synthesis with oligo(dT) or an mRNA-specificoligonucleotide primer; (2) polymerase chain reaction (PCR) in which oneor both oligonucleotides contains a phage promoter attached to asequence complementary to the region to be amplified; (3) transcriptionwith a phage promoter; and (4) reverse transcriptase-mediated dideoxysequencing of the transcript, which is primed with a nested (internal)oligonucleotide. In addition to revealing sequence information, thismethod can generate an in vitro translation product by incorporating atranslation initiation signal into the appropriate PCR primer: and canbe used to obtain novel mRNA sequence information from other species.

Substitution of Amino Acid(s):

The present invention provides active recombinant hybrid human/animaland animal/animal factor VIII molecules or fragments thereof comprisingat least one sequence including one or more unique amino acids of onespecies substituted for the corresponding amino acid sequence of theother species or fragments thereof, nucleic acid sequences encodingthese hybrids, methods for preparing and isolating them, and methods forcharacterizing their coagulant, immunogenic and immunoreactiveproperties.

The A2 domain is necessary for the procoagulant activity of the factorVIII molecule. Studies show that porcine factor VIII has six-foldgreater procoagulant activity than human factor VIII (Lollar, P. et al.(1991) J. Biol. Chem. 266:12481–12486, and that the difference incoagulant activity between human and porcine factor VIII appears to bebased on a difference in amino acid sequence between one or moreresidues in the human and porcine A2 domains (Lollar, P. et al. (1992)J. Biol. Chem. 267:23652–23657. Further, the A2 and C2 domains andpossibly a third light chain region in the human factor VIII moleculeare thought to harbor the epitopes to which most, if not all, inhibitoryantibodies react, according to Hoyer (1994) Semin. Hewatol. 31:1–5.

Recombinant hybrid human/animal, animal/animal, or equivalent factorVIII molecules or fragments thereof can be made by substitution of atleast one specific sequence including one or more unique amino acidsfrom the A2, C2, and/or other domains of the factor VIII of one speciesfor the corresponding sequence of the other species, wherein the aminoacid sequences differ, as illustrated in more detail below, between themolecules of the two species. In an exemplary preferred embodimentdescribed herein, the present invention provides active recombinanthybrid human/porcine factor VIII comprising porcine amino acid sequencesubstituted for corresponding human amino acid sequence that includes anepitope, wherein the hybrid factor VIII has decreased or noimmunoreactivity with inhibitory antibodies to factor VIII. In a furtherembodiment, active recombinant hybrid factor VIII molecules can also bemade comprising amino acid sequence from more than one speciessubstituted for the corresponding sequence in a third species.Recombinant hybrid equivalent molecules can also be made, comprisinghuman, animal, or hybrid factor VIII including at least one sequenceincluding one or more amino acids that have no known sequence identityto factor VIII, as further described below.

Any hybrid factor VIII construct having specific amino acid substitutionas described can be assayed by standard procedures for coagulantactivity and for reactivity with inhibitory antibodies to factor VIIIfor identification of hybrid factor VIII molecules with enhancedcoagulant activity and/or decreased antibody immunoreactivity. Hybridmolecules may also be identified that have reduced coagulant activitycompared to human or porcine factor VIII but also have decreasedantibody reactivity. One skilled in the art will recognize that hybridfactor VIII molecules or fragments thereof having less, equal, orgreater coagulant activity, compared to human or porcine factor VIII, isuseful for treating patients who have a factor VIII deficiency. Themethods described herein to prepare active recombinant hybridhuman/porcine factor VIII with substitution of specific amino acids canbe used to prepare active recombinant hybrid human/non-human,non-porcine mammalian factor VIII protein, hybrid animal-1/animal-2factor VIII, and hybrid equivalent factor VIII or fragments thereof.

Hybrid Factor VIII Molecules with Altered Coagulant Activity:

The present invention provides procoagulant recombinant hybridhuman/animal, animal/animal, or equivalent factor VIII molecules orfragments thereof comprising at least one specific sequence includingone or more unique amino acids having procoagulant activity in thefactor VIII of one species substituted for the corresponding amino acidsequence of the factor VIII of the other species, using establishedsite-directed mutagenesis techniques as described herein. The specificsequences to be used in the substitution are selected and the hybridconstructs are prepared and assayed for coagulant activity, as follows.Specifically provided as a preferred and exemplary embodiment is ahybrid human/porcine factor VIII comprising amino acid substitutions inthe A2 domain. It is understood that one skilled in the art can usethese methods to prepare other hybrid human/animal, animal/animal, andequivalent factor VIII molecules or fragments thereof having alteredcoagulant activity, preferably increased coagulant activity compared tohuman factor VIII.

The basis for the greater coagulant activity in porcine factor VIIIappears to be the more rapid spontaneous dissociation of the A2 subunitof human factor VIIIa than porcine factor VIIIa, which leads to loss ofactivity, according to Lollar, P. et al. (1990) J. Biol. Chem.265:1688–1692; Lollar, P. et al. (1992) J. Biol. Chem. 267:23652–23657;Fay, P. J. et al. (1992) J. Biol. Chem. 267:13246–13250.

A comparison of the alignment of the amino acid sequences of the humanand porcine factor VIII A2 domains (residue numbering starts at position373 with respect to the full length amino acid sequence of human factorVIII, SEQ ID NO:2) is shown in FIG. 1C. For preparation of a hybridhuman/porcine factor VIII molecule with altered coagulant activity, theinitial target candidates for mutagenesis, which were revealed uponcomparison of the human and porcine A2 amino acid sequences (SEQ ID NOs:2 and 6, respectively) within the human A2 domain, are shown in Table I.

TABLE I HUMAN AMINO ACID SEQUENCE TARGET CANDIDATES FOR MUTAGENESIS (SEQID NO: 2) Charge Sequence Residues Mismatches Changes 398–403 6 4 1434–444 10 4 3 484–496 13 7 3 598–603 6 4 2 536–541 6 4 0 713–722 10 6 2727–737 11 6 2

Table I and the bold letters of FIGS. 1A–1B illustrate seven sequencesin the human and pig A2 domain amino acid sequences (SEQ ID NOs:2 and 6,respectively) that constitute only 17 percent of the A2 domain butinclude 70 percent of the sequence differences between human and porcineA2 domains.

A recombinant hybrid human/porcine construct is described in which aminoacids Ser373-Glu604 in the A2 domain (Ser373-Arg740) of human factorVIII have been replaced with the homologous porcine sequence. Thisconstruct does not react with A2 inhibitors and has the same coagulantactivity as human B(−) factor VIII. A plasma-derived hybrid molecule isdescribed that comprises a complete porcine A2 domain substitution inthe human factor VIII that has increased coagulant activity compared tohuman factor VIII. Comparison of these constructs indicates that aregion between residues Asp605 and Arg740 is responsible for thedifference in activity between human and porcine factor VIII. Thisregion can be defined more specifically by systematically makingrecombinant hybrid human/porcine factor VIII molecules with porcinesubstitutions in the region between Asp605 and Arg740 by usingestablished site-directed mutagenesis techniques, for example, the“splicing by overlap extension” (SOE) method that has been usedextensively to make hybrid factor VIII molecules containing porcinesubstitutions in the NH₂-terminal region of A2. These molecules can beexpressed in COS-7 cells and baby hamster kidney cells as describedabove. They can be purified to homogeneity using methods known in theart, such as heparin-Sepharose™ and immunoaffinity chromatography.Protein concentration can be estimated by absorption of ultravioletlight at A₂₈₀, and the specific activity of the constructs can bedetermined by dividing coagulant activity (measured in units per ml bysingle stage clotting assay) by A₂₈₀. Human factor VIII has a specificactivity of approximately 3000–4000 U/A₂₈₀, whereas porcine factor VIIIhas a specific activity of approximately 20,000 U/A₂₈₀. In a preferredembodiment, the procoagulant recombinant hybrid human/porcine factorVIII has a specific activity of 20,000 U/A₂₈₀ and contains a minimalamount of porcine substitution in the A2 domain.

As described herein, site-directed mutagenesis techniques are used toidentify hybrid protein with coagulant activity that can be enhanced,equal to, or reduced, compared to human factor VIII, but preferably isenhanced. In the hybrid human/porcine embodiment, specific humansequences are replaced with porcine sequences, preferably using thesplicing by overlap extension method (SOE), as described by Ho, S. N.,et al., 77 Gene 51–59 (1994), and in Examples 7 and 8.Oligonucleotide-directed mutagenesis can also be used, as was done toloop out the amino acid sequence for part of the human A2 domain (seeExample 7). As functional analysis of the hybrids reveals coagulantactivity, the sequence can be further dissected and mapped forprocoagulant sequence by standard point mutation analysis techniques.

The present invention contemplates that hybrid factor VIII cDNA andprotein can be characterized by methods that are established androutine, such as DNA sequencing, coagulant activity assays, mass byELISA and by UV absorbance at 280 nm of purified hybrid factor VIII,specific coagulant activity (U/mg), SDS-PAGE of purified hybrid factorVIII, and the like. Other known methods of testing for clinicaleffectiveness may be required, such as amino acid, carbohydrate,sulfate, or metal ion analysis.

A recombinant hybrid factor VIII having superior coagulant activity,compared to human factor VIII, may be less expensive to make thanplasma-derived factor VIII and may decrease the amount of factor VIIIrequired for effective treatment of factor VIII deficiency.

Hybrid Factor VIII Molecules with Reduced Immunoreactivity:

Epitopes that are immunoreactive with antibodies that inhibit thecoagulant activity of factor VIII (“inhibitors” or “inhibitoryantibodies”) have been characterized based on known structure-functionrelationships in factor VIII. Presumably, inhibitors could act bydisrupting any of the macromolecular interactions associated with thedomain structure of factor VIII or its associations with von Willebrandfactor, thrombin, factor Xa, factor IXa, or factor X. However, over 90percent of inhibitory antibodies to human factor VIII act by binding toepitopes located in the 40 kDa A2 domain or 20 kDa C2 domain of factorVIII, disrupting specific functions associated with these domains, asdescribed by Fulcher et al. (1985) Proc. Natl. Acad. Sci USA82:7728–7732; and Scandella et al. (1988) Proc. Natl. Acad. Sci. USA85:6152–6156. In addition to the A2 and C2 epitopes, there may be athird epitope in the A3 or C1 domain of the light chain of factor VIII,according to Scandella et al. (1993) Blood 82:1767–1775. Thesignificance of this putative third epitope is unknown, but it appearsto account for a minor fraction of the epitope reactivity in factorVIII.

Anti-A2 antibodies block factor X activation, as shown by Lollar et al.(1994) J. Clin. Invest 93:2497–2504. Previous mapping studies bydeletion mutagenesis described by Ware et al. (1992) Blood Coagul.Fibrinolysis 3:703–716, located the A2 epitope to within a 20 kDa regionof the NH₂-terminal end of the 40 kDa A2 domain. Competitionimmunoradiometric assays have indicated that A2 inhibitors recognizeeither a common epitope or narrowly clustered epitopes, as described byScandella et al. (1992) Throm. Haemostas 67:665–671, and as demonstratedin Example 8.

The present invention provides active recombinant hybrid and hybridequivalent factor VIII molecules or fragments thereof, the nucleic acidsequences encoding these hybrids, methods of preparing and isolatingthem, and methods for characterizing them. These hybrids comprisehuman/animal, animal/animal, or equivalent hybrid factor VIII molecules,further comprising at least one specific amino acid sequence includingone or more unique amino acids of the factor VIII of one speciessubstituted for the corresponding amino acid sequence of the factor VIIIof the other species; or comprises at least one sequence including oneor more amino acids having no known sequence identity to factor VIIIsubstituted for specific amino acid sequence in human, animal, or hybridfactor VIII. The resulting hybrid factor VIII has reduced or noimmunoreactivity to factor VIII inhibitory antibodies, compared to humanor porcine factor VIII.

Using the approach described in the previous section for substitution ofamino acids in the factor VIII molecule, mutational analysis is employedto select corresponding factor VIII amino acid sequence of one species,preferably porcine, which is substituted for at least one sequenceincluding one or more amino acids in the factor VIII of another species,preferably human, or for amino acid sequence of a hybrid equivalentfactor VIII molecule, that includes one or more critical region(s) inthe A2, C2, or any other domain to which inhibitory antibodies aredirected. The methods are described in more detail below. The resultingprocoagulant recombinant hybrid construct has reduced or noimmunoreactivity to inhibitory antibodies, compared to human factorVIII, using standard assays. Through systematic substitution ofincreasingly smaller amino acid sequences followed by assay of thehybrid construct for immunoreactivity, as described below, the epitopein any domain of a factor VIII molecule is mapped, substituted by aminoacid sequence having less or no immunoreactivity, and a hybrid factorVIII is prepared.

It is understood that one skilled in the art can use this approachcombining epitope mapping, construction of hybrid factor VIII molecules,and mutational analysis of the constructs to identify and replace atleast one sequence including one or more amino acids comprising anepitope in the A2, C2, and/or other domains to which inhibitoryantibodies are directed and to construct procoagulant recombinant hybridhuman/animal, animal/animal, or equivalent factor VIII or fragmentsthereof having decreased or no immunoreactivity compared to human orporcine factor VIII. This approach is used, as described in Example 8,to prepare a recombinant procoagulant hybrid human/porcine factor VIIIhaving porcine amino acid substitutions in the human A2 domain and noantigenicity to anti-factor VIII antibodies as an exemplary embodiment.

Usually, porcine factor VIII has limited or no reaction with inhibitoryantibodies to human factor VIII. The recombinant hybrid human/porcinefactor VIII molecules having decreased or no reactivity with inhibitoryantibodies based on amino acid substitution in the A2 domain areprepared, as an example of how hybrid factor VIII can be prepared usingthe factor VIII of other species and substitutions in domains other thanA2, as follows. The porcine A2 domain is cloned by standard cloningtechniques, such as those described above and in Examples 6, 7, and 8,and then cut and spliced within the A2 domain using routine procedures,such as using restriction sites to cut the cDNA or splicing by overlapextension (SOE). The resulting porcine amino acid sequence issubstituted into the human A2 domain to form a hybrid factor VIIIconstruct, which is inserted into a mammalian expression vector,preferably ReNeo, stably transfected into cultured cells, preferablybaby hamster kidney cells, and expressed, as described above. The hybridfactor VIII is assayed for immunoreactivity, for example with anti-A2antibodies by the routine Bethesda assay or by plasma-free chromogenicsubstrate assay. The Bethesda unit (BU) is the standard method formeasuring inhibitor titers. If the Bethesda titer is not measurable(<0.7 BU/mg IgG) in the hybrid, then a human A2 epitope was eliminatedin the region of substituted corresponding porcine sequence. The epitopeis progressively narrowed, and the specific A2 epitope can thus bedetermined to produce a hybrid human/porcine molecule with as littleporcine sequence as possible. As described herein, a 25-residue sequencecorresponding to amino acids Arg484-IIe508 that is critical forinhibitory immunoreactivity has been identified and substituted in thehuman A2 domain. Within this sequence are only nine differences betweenhuman and porcine factor VIII. This region can be further analyzed andsubstituted.

Hybrid human/porcine factor VIII molecules having decreased or noreactivity with inhibitory antibodies based on substitution of aminoacid sequence in the C1, C2 or other domain, with or withoutsubstitution in the A2 domain, can also be prepared. The C2 epitope, forexample can be mapped using the homolog scanning approach combined withsite-directed mutagensesis. More specifically, the procedures can be thesame or similar to those described herein for amino acids substitutionin the A2 domain, including cloning the porcine C2 or other domain, forexample by using RT-PCR or by probing a porcine liver cDNA library withhuman C2 or other domain DNA; restriction site techniques and/orsuccessive SOE to map and simultaneously replace epitopes in the C2 orother domain; substitution for the human C2 or other domain in B(−)factor VIII; insertion into an expression vector, such as pBluescript;expression in cultured cells; and routine assay for immunoreactivity.For the assays, the reactivity of C2 hybrid factor VIII with aC2-specific inhibitor, MR [Scandella et al. (1992) Thomb. Haemostasis67:665–671 and Lubin et al. (1994)], and/or other C2 specific antibodiesprepared by affinity chromatography can be performed.

The C2 domain consists of amino acid residues 2173–2332 (SEQ ID NO:2).Within this 154 amino acid region, inhibitor activity appears to bedirected to a 65 amino acid region between residues 2248 and 2312,according to Shima, M. et al. (1993) Thromb. Haemostas 69:240–246. Ifthe C2 sequence of human and porcine factor VIII is approximately 85percent identical in this region, as it is elsewhere in the functionallyactive regions of factor VIII, there will be approximately tendifferences between human and porcine factor VIII C2 amino acidsequence, which can be used as initial targets to construct hybrids withsubstituted C2 sequence.

It is likely that clinically significant factor VIII epitopes areconfined to the A2 and C2 domains. However, if antibodies to otherregions (A1, A3, B, or C1 domains) of factor VIII are identified, theepitopes can be mapped and eliminated by using the approach describedherein for the nonantigenic hybrid human/porcine factor VIII molecules.

More specifically, mapping of the putative second light chain epitopeand/or any other epitope in any other animal or human factor VIII domaincan also be accomplished. Initially, determination of the presence of athird inhibitor epitope in the A3 or C1 domains can be made as follows.Using human (“H”) and porcine (“p”) factor VIII amino acid sequences asa model, A1_(p)-A2_(p)-A3_(p)-C1_(H)-C2_(p) and A1_(p)-A2_(p)-A3_(H)-C1_(p)-C2_(p) B-domainless hybrids will be constructed. Inhibitor IgGfrom approximately 20 patient plasmas (from Dr. Dorothea Scandella,American Red Cross) who have low or undetectable titers against porcinefactor VIII will be tested against the hybrids. If the third epitope isin the A3 domain, inhibitory IgG is expected to react withA1_(p)-A2_(p)-A3_(H)-C1_(p)-C2_(p) but notA1_(p)-A2_(p)-A3_(p)-C1_(H)-C2_(p). Conversely, if the third epitope isin the C1 domain, then inhibitory IgG is expected to react withA1_(p)-A2_(p)-A3_(p)-C1_(H)-C2_(p) but notA1_(p)-A2_(p)-A3_(H)-C1_(p)-C2_(p). If a third epitope is identified itwill be characterized by the procedures described herein for the A2 andC2 epitopes.

For example, antibodies specific for the C1 or A3 domain epitope can beisolated from total patient IgG by affinity chromatography using theA1_(p)-A2_(p)-A3_(H)-C1_(p)-C2_(p) and A1_(p)-A2_(p)-A3_(p)-C1_(H)-C²_(p) hybrids, and by elimination of C2 specific antibodies by passageover recombinant factor VIII C2-Sepharaose™. The putative third epitopewill be identified by SOE constructs in which, in a preferredembodiment, portions of the human factor VIII A3 or C1 domain aresystematically replaced with porcine sequence.

Hybrid Factor VIII Molecules with Reduced Immunogenicity:

A molecule is immunogenic when it can induce the production ofantibodies in human or animal. The present invention provides aprocoagulant recombinant hybrid human/animal or animal/animal factorVIII molecule, hybrid factor VIII equivalent molecule, or fragment ofeither that is less immunogenic than wild-type human porcine factor VIIIin human or animal, comprising at least one specific amino acid sequenceincluding one or more unique amino acids of the factor VIII of onespecies substituted for the corresponding amino acid sequence that hasimmunogenic activity of the factor VIII of the other species; or atleast one amino acid sequence including one or more amino acids havingno known identity to factor VIII substituted for amino acid sequence ofthe human, animal, or hybrid factor. This hybrid can be used to lowerthe incidence of inhibitor development in an animal or human and totreat factor VIII deficiency, and would be preferred in treatingpreviously untreated patients with hemophilia. In a preferredembodiment, the hybrid factor VIII comprises human factor VIII aminoacid sequence, further comprising one or more alanine residuessubstituted for human amino acid sequence having immunogenic activity,resulting in a procoagulant recombinant hybrid equivalent molecule orfragment thereof having reduced or no immunogenicity-in human or animal.

The process described herein of epitope mapping and mutational analysiscombined with substitution of non-antigenic amino acid sequence in afactor VIII molecule, using hybrid human/porcine factor VIII, produceshybrid molecules with low antigenicity. Using this model and theassociated methods, any of the hybrid constructs described herein can bealtered by site-directed mutagenesis techniques to remove as much of anyfunctional epitope as possible to minimize the ability of the immunesystem to recognize the hybrid factor VIII, thereby decreasing itsimmunogenicity.

One method that can be used to further reduce the antigenicity and toconstruct a less immunogenic hybrid factor VIII is alanine scanningmutagenesis, described by Cunningham, B. C. et al. (1989) Science244:1081–1085, of selected specific amino acid sequences in human,animal, or hybrid equivalent factor VIII. In alanine scanningmutagenesis, amino acid side chains that are putatively involved in anepitope are replaced by alanine residues by using site-directedmutagenesis. By comparing antibody binding of alanine mutants towild-type protein, the relative contribution of individual side chainsto the binding interaction can be determined. Alanine substitutions arelikely to be especially useful, since side chain contributions toantibody binding are eliminated beyond the β carbon, but, unlike glycinesubstitution, main chain conformation is not usually altered. Alaninesubstitution does not impose major steric, hydrophobic or electrostaticeffects that dominate protein-protein interactions.

In protein antigen-antibody interactions, there usually are about 15–20antigen side chains in contact with the antibody. Side chaininteractions, as opposed to main chain interactions, dominateprotein-protein interactions. Recent studies have suggested that only afew (approximately 3 to 5) of these side chain interactions contributemost of the binding energy. See Clackson, T. et al. (1995) Science267:383–386. An extensive analysis of growth hormone epitopes forseveral murine monoclonal antibodies revealed the following hierarchyfor side chain contributions to the binding energy:Arg>Pro>Glu-Asp-Phe-IIe, with Trp, Ala, Gly, and Cys not tested [Jin, L.et al. (1992) J. Mol. Biol. 226:851–865]. Results with the A2 epitopedescribed herein are consistent with this, since twelve of the 25residues in the 484–508 A2 segment contain these side chains (Table 1).

The finding that certain amino acid residues are particularly wellrecognized by antibodies, indicates that elimination of these residuesfrom a known epitope can decrease the ability of the immune system torecognize these epitopes, i.e., can make a molecule less immunogenic. Inthe case of the A2 epitope, immunogenic residues can be replaced withoutloss of factor VIII coagulant activity. For example, in HP9, Arg484 isreplaced by Ser, Pro485 is replaced by Ala, Arg489 is replaced by Gly,Pro492 is replaced by Leu, and Phe501 is replaced by Met. Further,results from the patient plasmas used to test immunoreactivity in hybridhuman/porcine factor VIII constructs, described in Example 8, indicatethat antibodies from different patients recognize the same or a verysimilar structural region in the A2 domain and that the residues in theA2 domain that participate in binding A2 inhibitors appear to showlittle variation. Thus, the A2 epitope included in human factor VIIIresidues 484–508 is an immunodominant epitope in that it is recognizedby the human immune system better than other structural regions offactor VIII. Replacing this structure by nonantigenic factor VIIIsequence from another species or by non-factor VIII amino acid sequence,while retaining full procoagulant activity, is expected to alterrecognition of hybrid or hybrid equivalent factor VIII by the immunesystem.

It is anticipated that site-directed mutagenesis to replace bulky and/orcharged residues that tend to dominate epitopes with small, neutral sidechains (e.g., alanine) may produce a less immunogenic region. It isexpected that a molecule containing a few of these substitutions at eachsignificant inhibitor epitope will be difficult for the immune system tofit by the lock-and-key mechanism that is typical of antigen-antibodyinteractions. Because of its low antigenicity, such a hybrid moleculecould be useful in treating factor VIII deficiency patients withinhibitors, and because of its low immunogenicity, it could be useful intreating previously untreated patients with hemophilia A.

A general result is that mutation of one of a few key residues issufficient to decrease the binding constant for a given protein-proteininteraction by several orders of magnitude. Thus, it appears likely thatall factor VIII epitopes contain a limited number of amino acids thatare critical for inhibitor development. For each epitope in factor VIII,alanine substitutions for at least one sequence including one or morespecific amino acids having immunogenic activity, may produce an activemolecule that is less immunogenic than wild-type factor VIII. In apreferred embodiment, the hybrid factor VIII is B-domainless.

The methods for preparing active recombinant hybrid or hybrid equivalentfactor VIII with substitution of amino acid sequence having little or noimmunogenic activity for amino acid sequence in the factor VIII havingimmunogenic activity are as follows, using hybrid human/porcine factorVIII with amino acid substitutions in the A2 domain as an exemplaryembodiment. There are 25 residues in the human factor VIII region484–508. Site-directed mutagenesis can be used to make single mutants inwhich any of these residues is replaced by any of the other 19 aminoacids for a total of 475 mutants. Furthermore, hybrid molecules havingmore than one mutation can be constructed.

The hybrid constructs can be assayed for antigenicity by measuring thebinding constant for inhibitor antibodies, as described by Friguet, B.et al. (1985) J. Immunol. Methods 77:305–319 (1985). In a preferredembodiment, the binding constant will be reduced by at least threeorders of magnitude, which would lower the Bethesda titer to a levelthat is clinically insignificant. For example, the IC₅₀ (a crude measureof the binding constant) of inhibition by A2 antibodies was reduced inhybrid human/porcine factor VIII constructs HP2, HP4, HP5, HP7, and HP9,described in Example 8, and this was associated with a reduction inBethesda titer to an unmeasurable level. It is anticipated, for example,that a double or triple alanine mutant of human factor VIII (e.g., ahuman factor VIII Arg484->Ala, Arg489->Ala, Phe501->Ala triple mutant)will produce a molecule with sufficiently low antigenicity fortherapeutic use. Similar mutations can be made in the C2 epitope and theputative third epitope. A preferred embodiment comprises two or threealanine substitutions into two or three factor VIII epitopes. Othersubstitutions into these regions can also be done.

In a preferred embodiment, hybrid equivalent factor VIII molecules willbe identified that are less antigenic and/or immunogenic in human andanimal than either human or porcine factor VIII. Such hybrid equivalentconstructs can be tested in animals for their reduced antigenicityand/or immunogenicity. For example, control and factor VIII deficientrabbits, pigs, dogs, mice, primates, and other mammals can be used asanimal models. In one experimental protocol, the hybrid or hybridequivalent factor VIII can be administered systematically over a periodof six months to one year to the animal, preferably by intravenousinfusion, and in a dosage range between 5 and 50 Units/kg body weight,preferably 10–50 Units/kg, and most preferably 40 Units/kg body weight.Antibodies can be measured in plasma samples taken at intervals afterthe infusions over the duration of the testing period by routinemethods, including immunoassay and the Bethesda assay. Coagulantactivity can also be measured in samples with routine procedures,including a one-stage coagulation assay.

The hybrid equivalent factor VIII molecules can be tested in humans fortheir reduced antigenicity and/or immunogenicity in at least two typesof clinical trials. In one type of trial, designed to determine whetherthe hybrid or hybrid equivalent factor VIII is immunoreactive withinhibitory antibodies, hybrid or hybrid equivalent factor VIII isadministered, preferably by intravenous infusion, to approximately 25patients having factor VIII deficiency who have antibodies to factorVIII that inhibit the coagulant activity of therapeutic human or porcinefactor VIII. The dosage of the hybrid or hybrid equivalent factor VIIIis in a range between 5 and 50 Units/kg body weight, preferably 10–50Units/kg, and most preferably 40 Units/kg body weight. Approximately 1hour after each administration, the recovery of factor VIII from bloodsamples is measured in a one-stage coagulation assay. Samples are takenagain approximately 5 hours after infusion, and recovery is measured.Total recovery and the rate of disappearance of factor VIII from thesamples is predictive of the antibody titer and inhibitory activity. Ifthe antibody titer is high, factor VIII recovery usually cannot bemeasured. The recovery results are compared to the recovery of recoveryresults in patients treated with plasma-derived human factor VIII,recombinant human factor VIII, porcine factor VIII, and other commonlyused therapeutic forms of factor VIII or factor VIII substitutes.

In a second type of clinical trial, designed to determine whether thehybrid or hybrid equivalent factor VIII is immunogenic, i.e., whetherpatients will develop inhibitory antibodies, hybrid or hybrid equivalentfactor VIII is administered, as described in the preceding paragraph, toapproximately 100 previously untreated hemophiliac patients who have notdeveloped antibodies to factor VIII. Treatments are given approximatelyevery 2 weeks over a period of 6 months to 1 year. At 1 to 3 monthintervals during this period, blood samples are drawn and Bethesdaassays or other antibody assays are performed to determine the presenceof inhibitory antibodies. Recovery assays can also be done, as describedabove, after each infusion. Results are compared to hemophiliac patientswho receive plasma-derived human factor VIII, recombinant human factorVIII, porcine factor VIII, or other commonly used therapeutic forms offactor VIII or factor VIII substitutes.

Preparation of Hybrid Factor VIII Molecules Using Human and Non-porcine,Non-human Mammalian Factor VIII Amino Acid Sequence:

The methods used to prepare hybrid human/porcine factor VIII withsubstitution of specific amino acids can be used to prepare recombinanthybrid human/non-human, non-porcine mammalian or animal/animal factorVIII protein that has, compared to human or porcine factor VIII, alteredor the same coagulant activity and/or equal or reduced immunoreactivityand/or immunogenicity, based on substitution of one or more amino acidsin the A2, C2, and/or other domains.

Similar comparisons of amino acid sequence identity can be made betweenhuman and non-human, non-porcine mammalian factor VIII proteins todetermine the amino acid sequences in which procoagulant activity,anti-A2 and anti-C2 immunoreactivity, and or immunogenicity, orimmunoreactivity and/or immunogenicity in other domains reside. Similarmethods can then be used to prepare hybrid human/non-human, non-porcinemammalian factor VIII molecules. As described above, functional analysisof each hybrid will reveal those with decreased reactivity to inhibitoryantibodies, and/or reduced immunogenicity, and/or increased coagulantactivity, and the sequence can be further dissected by point mutationanalysis.

For example, hybrid human/mouse factor VIII molecules can be prepared asdescribed above. The amino acid sequence alignment of the A2 domain ofhuman (SEQ ID NO:2) and mouse (SEQ ID NO:6) is shown in FIG. 1C. Asreported by Elder et al., the factor VIII protein encoded by the mousecDNA (SEQ ID NO:5) has 2319 amino acids, with 74% sequence identityoverall to the human sequence (SEQ ID NO:2) (87 percent identity whenthe B domain is excluded from the comparison), and is 32 amino acidsshorter than human factor VIII. The amino acid sequences in the mouse Aand C domains (SEQ ID NO:6) are highly conserved, with 84–93 percentsequence identity to the human sequence (SEQ ID NO:2), while the B andthe two short acidic domains have 42–70 percent sequence identity.Specifically, the A1, A2, and A3 mouse amino acid sequences (SEQ ID NO:6) are 85, 85, and 90 percent identical to the corresponding human aminoacid sequences (SEQ ID NO:2). The C1 and C2 mouse amino acid sequencesare 93 and 84 percent identical to the corresponding human amino acidsequences. In the predicted mouse factor VIII amino acid sequence (SEQID NO: 6), the A1, A2, and A3 domains are homologous to human factorVIII amino acids 1–372, 373–740, and 1690–2032, respectively, usingamino acid sequence identity for numbering purposes.

The thrombin/factor Xa and all but one activated protein C cleavagesites are conserved in mouse factor VIII. The tyrosine residue for vonWillebrand factor binding is also conserved.

According to Elder et al., the nucleotide sequence (SEQ ID NO:5) ofmouse factor VIII contains 7519 bases and has 67 percent identityoverall with the human nucleotide sequence (SEQ ID NO:1). The 6957 basepairs of murine coding sequence have 82 percent sequence identity withthe 7053 base pairs of coding sequence in human factor VIII. When the Bdomain is not included in the comparison, there is an 88 percentnucleotide sequence identity.

Elder et al. report that human and mouse factor VIII molecules are 74percent identical overall, and that 95 percent of the human residuesthat lead to hemophilia when altered are identical in the mouse. Thesedata support the application of the same techniques used to identifyamino acid sequence with coagulant activity and/or immunoreactivity toantibodies in the porcine factor VIII molecule to the mouse or otheranimal factor VIII to identify similar amino acid sequences and preparehybrid molecules.

Preparation of Hybrid Factor VIII Molecules Having ReducedCross-reactivity Using Human and Non-human, Non-porcine Mammalian FactorVIII Amino Acid Sequence and Non-factor VIII Amino Acid Sequence:

Porcine factor VIII is used clinically to treat factor VIII deficiencypatients who have inhibitory antibodies to human factor VIII.Cross-reactivity, in which human plasma reacts with porcine factor VIII,can be reduced by preparation of hybrid porcine/non-human, non-porcinemammalian or hybrid equivalent factor VIII. In a preferred embodiment, adetermination of whether human A2, C2, or other domain-specificinhibitors react with non-human, non-porcine mammalian (“othermammalian”) factor VIII is made, using the routine Bethesda assay andthe particular other mammalian plasma as the standard. Inhibitor titersare usually measured in plasma, so purified other mammalian factor VIIIis not necessary. If the inhibitors do not react with the othermammalian factor VIII, such as murine factor VIII, the sequence of whichis known, then corresponding other mammalian sequence can be substitutedinto the porcine epitope region, as identified by using human/porcinehybrids. Once the animal sequence is known, site directed mutagenesistechniques, such as oligonucleotide-mediated mutagenesis described byKunkel, T. A. et al. (1991) Meth. Enzymol 204: 125–139, can be used toprepare the hybrid porcine/animal factor VIII molecule. If other animalplasmas are less reactive with A2, C2, or other factor VIII inhibitorsthan murine or porcine factor VIII, the animal sequence corresponding tothe porcine epitope can be determined by routine procedures, such asRT-PCR, and a hybrid human/animal or porcine/animal factor VIIIconstructed by site-directed mutagenesis. Also, hybrid human/animal orporcine/non-porcine mammalian factor VIII having reducedcross-reactivity with human plasma compared to porcine factor VIII canbe prepared that has corresponding amino acid sequence substitution fromone or more other animals. In a further embodiment, cross-reactivity canbe reduced by substitution of amino acid sequence having no knownidentity to factor VIII amino acid sequence, preferably alanine residuesusing alanine scanning mutagenesis techniques, for porcine epitopesequence.

After identification of clinically significant epitopes, recombinanthybrid factor VIII molecules will be expressed that have less than orequal cross-reactivity compared with porcine factor VIII when tested invitro against a broad survey of inhibitor plasmas. Preferably thesemolecules will be combined A2/C2 hybrids in which immunoreactive aminoacid sequence in these domains is replaced by other mammalian sequence.Additional mutagenesis in these regions may be done to reducecross-reactivity. Reduced cross-reactivity, although desirable, is notnecessary to produce a product that may have advantages over theexisting porcine factor VIII concentrate, which produces side effectsdue to contaminant porcine proteins and may produce untoward effects dueto the immunogenicity of porcine factor VIII sequences. A hybridhuman/other mammalian or porcine/other mammalian factor VIII moleculewill not contain foreign porcine proteins. Additionally, the extensiveepitope mapping accomplished in the porcine A2 domain indicates thatgreater than 95% of the therapeutic hybrid human/porcine factor VIIIsequence will be human.

Preparation of Hybrid Factor VIII Equivalents:

The methods for amino acid substitution in factor VIII moleculesdescribed above and in the examples can also be used to prepareprocoagulant recombinant hybrid factor VIII equivalent molecules orfragments thereof comprising at least one amino acid sequence includingone or more amino acids having no known amino acid sequence identity tofactor VIII (“non-factor VIII sequence”) substituted for at least onespecific amino acid sequence that includes an antigenic and/orimmunogenic site in human, animal, or hybrid factor VIII. The resultingactive hybrid factor VIII equivalent molecule has equal or lessreactivity with factor VIII inhibitory antibodies and/or lessimmunogenicity in human and animals than the unsubstituted human,animal, or hybrid factor VIII.

Suitable amino acid residues that can be substituted for those sequencesof amino acids critical to coagulant and/or antigenic and/or immunogenicactivity in human or animal factor VIII or hybrid human/animal factorVIII to prepare a hybrid equivalent factor VIII molecule include anyamino acids having no known sequence identity to animal or human factorVIII amino acid sequence that has coagulant, antigenic, or immunogenicactivity. In a preferred embodiment, the amino acids that can besubstituted include alanine residues using alanine scanning mutagenesistechniques.

Hybrid factor VIII equivalent molecules described herein also includethose molecules in which amino acid residues having no known identity toanimal factor VIII sequence are substituted for amino acid residues notcritical to coagulant, antigenic, or immunogenic activity.

As described above, in one embodiment of a hybrid factor VIII equivalentmolecule, the molecule has reduced cross-reactivity with inhibitorplasmas. One or more epitopes in the cross-reactive factor VIII areidentified, as described above, and then replaced by non-factor VIIIamino acid sequence, preferably alanine residues, using, for example,the alanine scanning mutagenesis method.

In a preferred embodiment, a procoagulant recombinant hybrid factor VIIIequivalent molecule is prepared comprising at least one sequenceincluding one or more amino acids having no known sequence identity tofactor VIII, preferably alanine residues, substituted for at least onesequence including one or more amino acids including an epitope, and/orfor at least one sequence including one or more amino acids including animmunogenic site, preferably in human factor VIII. The resulting hybridequivalent factor VIII molecule or fragment thereof has reduced or noimmunoreactivity with inhibitory antibodies to factor VIII and/orreduced or no immunogenicity in human or animals. The methods foridentifying specific antigenic amino acid sequence in the A2 domain ofhuman factor VIII for substitution by nonantigenic porcine unique aminoacid sequence are described in Examples 7 and 8 and are exemplary foridentifying antigenic sequence in the A2 and other domains of human andanimal factor VIII and for using site-directed mutagenesis methods suchas alanine scanning mutagenesis to substitute non-factor VIII amino acidsequence.

Since the human A2 epitope has been narrowed to 25 or few amino acids,as described in Example 8, alanine scanning mutagenesis can be performedon a limited number of hybrid factor VIII constructs having human aminoacid sequence to determine which are procoagulant, non-immunoreactiveand/or nonimmunogenic hybrid factor VIII constructs based on A2 aminoacid substitutions. In the A2 domain, the most likely candidates foralanine substitutions to achieve both reduced antigenicity andimmunogenicity in the hybrid construct are Arg484, Pro485, Tyr487,Ser488, Arg489, Pro492, Val495, Phe501, and IIe508. The binding affinityof a hybrid construct comprising each of these mutants for mAb413 and apanel of A2 specific patient IgGs will be determined by ELISA. Anymutant that is active and has a binding affinity for A2 inhibitors thatis reduced by more than 2 orders of magnitude is a candidate for the A2substituted factor VIII molecule. Constructs having more than onemutation will be selected, based on the assumption that the more theepitope is altered, the less immunogenic it will be. It is possible thatthere are other candidate residues in the region between Arg484-IIe508,since there may be key residues for the epitope that are common to bothhuman and porcine factor VIII. For example, charged residues arefrequently involved in protein-protein interactions and, in fact, analanine substitute for Arg490 produces a factor VIII procoagulatedhaving only 0.2% of the reactivity to inhibitor of human factor VIII(Table VI). Similarly, an alanine substitution for Lys493 is a possiblecandidate.

This procedure will be carried out in the C2 epitope and the putativethird epitope, which is thought to be in the A3 or C1 domains, as wellas any other epitopes identified in factor VIII, to prepare hybridequivalent factor VIII constructs.

Diagnostic Assays.

The hybrid human/animal, animal/animal, or equivalent factor VIII cDNAand/or protein expressed therefrom, in whole or in part, can be used inassays as diagnostic reagents for the detection of inhibitory antibodiesto human or animal factor VIII or to hybrid human/animal factor orequivalent VIII in substrates, including, for example, samples of serumand body fluids of human patients with factor VIII deficiency. Theseantibody assays include assays such as ELISA assays, immunoblots,radioimmunoassays, immunodiffusion assays, and assay of factor VIIIbiological activity (e.g., by coagulation assay). Techniques forpreparing these reagents and methods for use thereof are known to thoseskilled in the art. For example, an immunoassay for detection ofinhibitory antibodies in a patient serum sample can include reacting thetest sample with a sufficient amount of the hybrid human/animal factorVIII that contains at least one antigenic site, wherein the amount issufficient to form a detectable complex with the inhibitory antibodiesin the sample.

Nucleic acid and amino acid probes can be prepared based on the sequenceof the hybrid human/porcine, human/non-human, non-porcine mammalian,animal/animal, or equivalent factor VIII cDNA or protein molecule orfragments thereof. In some embodiments, these can be labeled using dyesor enzymatic, fluorescent, chemiluminescent, or radioactive labels thatare commercially available. The amino acid probes can be used, forexample, to screen sera or other body fluids where the presence ofinhibitors to human, animal, or hybrid human/animal factor VIII issuspected. Levels of inhibitors can be quantitated in patients andcompared to healthy controls, and can be used, for example, to determinewhether a patient with a factor VIII deficiency can be treated with ahybrid human/animal or hybrid equivalent factor VIII. The cDNA probescan be used, for example, for research purposes in screening DNAlibraries.

Pharmaceutical Compositions.

Pharmaceutical compositions containing hybrid human/animal,porcine/non-human, non-porcine mammalian, animal-1/animal-2, orequivalent factor VIII, alone or in combination with appropriatepharmaceutical stabilization compounds, delivery vehicles, and/orcarrier vehicles, are prepared according to known methods, as describedin Remington's Pharmaceutical Sciences by E. W. Martin.

In one preferred embodiment, the preferred carriers or delivery vehiclesfor intravenous infusion are physiological saline or phosphate bufferedsaline.

In another preferred embodiment, suitable stabilization compounds,delivery vehicles, and carrier vehicles include but are not limited toother human or animal proteins such as albumin.

Phospholipid vesicles or liposomal suspensions are also preferred aspharmaceutically acceptable carriers or delivery vehicles. These can beprepared according to methods known to those skilled in the art and cancontain, for example, phosphatidylserine/-phosphatidylcholine or othercompositions of phospholipids or detergents that together impart anegative charge to the surface, since factor VIII binds to negativelycharged phospholipid membranes. Liposomes may be prepared by dissolvingappropriate lipid(s) (such as stearoyl phosphatidyl ethanolamine,stearoyl phosphatidyl choline, arachadoyl phosphatidyl choline, andcholesterol) in an inorganic solvent that is then evaporated, leavingbehind a thin film of dried lipid on the surface of the container. Anaqueous solution of the hybrid factor VIII is then introduced into thecontainer. The container is then swirled by hand to free lipid materialfrom the sides of the container and to disperse lipid aggregates,thereby forming the liposomal suspension.

The hybrid factor or hybrid equivalent factor VIII can be combined withother suitable stabilization compounds, delivery vehicles, and/orcarrier vehicles, including vitamin K dependent clotting factors, tissuefactor, and von Willebrand factor (vWf) or a fragment of vWf thatcontains the factor VIII binding site, and polysaccharides such assucrose.

Hybrid or hybrid equivalent factor VIII can also be delivered by genetherapy in the same way that human factor VIII can be delivered, usingdelivery means such as retroviral vectors. This method consists ofincorporation of factor VIII cDNA into human cells that are transplanteddirectly into a factor VIII deficient patient or that are placed in animplantable device, permeable to the factor VIII molecules butimpermeable to cells, that is then transplanted. The preferred methodwill be retroviral-mediated gene transfer. In this method, an exogenousgene (e.g., a factor VIII cDNA) is cloned into the genome of a modifiedretrovirus. The gene is inserted into the genome of the host cell byviral machinery where it will be expressed by the cell. The retroviralvector is modified so that it will not produce virus, preventing viralinfection of the host. The general principles for this type of therapyare known to those skilled in the art and have been reviewed in theliterature [e.g., Kohn, D. B. et al. (1989) Transufusion 29:812–820].

Hybrid factor VIII can be stored bound to vWf to increase the half-lifeand shelf-life of the hybrid molecule. Additionally, lyophilization offactor VIII can improve the yields of active molecules in the presenceof vWf. Current methods for storage of human and animal factor VIII usedby commercial suppliers can be employed for storage of hybrid factorVIII. These methods include: (1) lyophilization of factor VIII in apartially-purified state (as a factor VIII “concentrate” that is infusedwithout further purification); (2) immunoaffinity-purification of factorVIII by the Zimmerman method and lyophilization in the presence ofalbumin, which stabilizes the factor VIII; (3) lyophilization ofrecombinant factor VIII in the presence of albumin.

Additionally, hybrid factor VIII has been indefinitely stable at 4° C.in 0.6 M NaCl, 20 mM MES, and 5 mM CaCl₂ at pH 6.0 and also can bestored frozen in these buffers and thawed with minimal loss of activity.

Methods of Treatment.

Hybrid or hybrid equivalent factor VIII is used to treat uncontrolledbleeding due to factor VIII deficiency (e.g., intraarticular,intracranial, or gastrointestinal hemorrhage) in hemophiliacs with andwithout inhibitory antibodies and in patients with acquired factor VIIIdeficiency due to the development of inhibitory antibodies. The activematerials are preferably administered intravenously.

Additionally, hybrid or hybrid equivalent factor VIII can beadministered by transplant of cells genetically engineered to producethe hybrid or by implantation of a device containing such cells, asdescribed above.

In a preferred embodiment, pharmaceutical compositions of hybrid orhybrid equivalent factor VIII alone or in combination with stabilizers,delivery vehicles, and/or carriers are infused into patientsintravenously according to the same procedure that is used for infusionof human or animal factor VIII.

The treatment dosages of hybrid or hybrid equivalent factor VIIIcomposition that must be administered to a patient in need of suchtreatment will vary depending on the severity of the factor VIIIdeficiency. Generally, dosage level is adjusted in frequency, duration,and units in keeping with the severity and duration of each patient'sbleeding episode. Accordingly, the hybrid factor VIII is included in thepharmaceutically acceptable carrier, delivery vehicle, or stabilizer inan amount sufficient to deliver to a patient a therapeutically effectiveamount of the hybrid to stop bleeding, as measured by standard clottingassays.

Factor VIII is classically defined as that substance present in normalblood plasma that corrects the clotting defect in plasma derived fromindividuals with hemophilia A. The coagulant activity in vitro ofpurified and partially-purified forms of factor VIII is used tocalculate the dose of factor VIII for infusions in human patients and isa reliable indicator of activity recovered from patient plasma and ofcorrection of the in vivo bleeding defect. There are no reporteddiscrepancies between standard assay of novel factor VIII molecules invitro and their behavior in the dog infusion model or in human patients,according to Lusher, J. M. et al. 328 New Engl. J. Med. 328:453–459;Pittman, D. D. et al. (1992) Blood 79:389–397; and Brinkhous et al.(1985) Proc. Natl. Acad. Sci. 82:8752–8755.

Usually, the desired plasma factor VIII level to be achieved in thepatient through administration of the hybrid or hybrid equivalent factorVIII is in the range of 30–100% of normal. In a preferred mode ofadministration of the hybrid or hybrid equivalent factor VIII, thecomposition is given intravenously at a preferred dosage in the rangefrom about 5 to 50 units/kg body weight, more preferably in a range of10–50 units/kg body weight, and most preferably at a dosage of 20–40units/kg body weight; the interval frequency is in the range from about8 to 24 hours (in severely affected hemophiliacs); and the duration oftreatment in days is in the range from 1 to 10 days or until thebleeding episode is resolved. See, e.g., Roberts, H. R., and M. R.Jones, “Hemophilia and Related Conditions—Congenital Deficiencies ofProthrombin (Factor II, Factor V, and Factors VII to XII),” Ch. 153,1453–1474, 1460, in Hematology, Williams, W. J., et al., ed. (1990).Patients with inhibitors may require more hybrid or hybrid equivalentfactor VIII, or patients may require less hybrid or hybrid equivalentfactor VIII because of its higher specific activity than human factorVIII or decreased antibody reactivity or immunogenicity. As in treatmentwith human or porcine factor VIII, the amount of hybrid or hybridequivalent factor VIII infused is defined by the one-stage factor VIIIcoagulation assay and, in selected instances, in vivo recovery isdetermined by measuring the factor VIII in the patient's plasma afterinfusion. It is to be understood that for any particular subject,specific dosage regimens should be adjusted over time according to theindividual need and the professional judgment of the personadministering or supervising the administration of the compositions, andthat the concentration ranges set forth herein are exemplary only andare not intended to limit the scope or practice of the claimedcomposition.

Treatment can take the form of a single intravenous administration ofthe composition or periodic or continuous administration over anextended period of time, as required. Alternatively, hybrid or hybridequivalent factor VIII can be administered subcutaneously or orally withliposomes in one or several doses at varying intervals of time.

Hybrid or hybrid equivalent factor VIII can also be used to treatuncontrolled bleeding due to factor VIII deficiency in hemophiliacs whohave developed antibodies to human factor VIII. In this case, coagulantactivity that is superior to that of human or animal factor VIII aloneis not necessary. Coagulant activity that is inferior to that of humanfactor VIII (i.e., less than 3,000 units/mg) will be useful if thatactivity is not neutralized by antibodies in the patient's plasma.

The hybrid or hybrid equivalent factor VIII molecule and the methods forisolation, characterization, making, and using it generally describedabove will be further understood with reference to the followingnon-limiting examples.

EXAMPLE 1 Assay of Porcine Factor VIII and Hybrid Human/Porcine FactorVIII

Porcine factor VIII has more coagulant activity than human factor VIII,based on specific activity of the molecule. These results are shown inTable III in Example 4. This conclusion is based on the use ofappropriate standard curves that allow human porcine factor VIII to befairly compared. Coagulation assays are based on the ability of factorVIII to shorten the clotting time of plasma derived from a patient withhemophilia A. Two types of assays were employed: the one-stage and thetwo stage assay.

In the one-stage assay, 0.1 ml hemophilia A plasma (George KingBiomedical, Inc.) was incubated with 0.1 ml activated partialthromboplastin reagent (APTT) (Organon Teknika) and 0.01 ml sample orstandard, consisting of diluted, citrated normal human plasma, for 5 minat 37° C. in a water bath. Incubation was followed by addition of 0.1 ml20 mM CaCl₂, and the time for development of a fibrin clot wasdetermined by visual inspection.

A unit of factor VIII is defined as the amount present in 1 ml ofcitrated normal human plasma. With human plasma as the standard, porcineand human factor VIII activity were compared directly. Dilutions of theplasma standard or purified proteins were made into 0.15 M NaCl, 0.02 MHEPES, pH 7.4. The standard curve was constructed based on 3 or 4dilutions of plasma, the highest dilution being 1/50, and on log₁₀clotting time plotted against log₁₀ plasma concentration, which resultsin a linear plot. The units of factor VIII in an unknown sample weredetermined by interpolation from the standard curve.

The one-stage assay relies on endogenous activation of factor VIII byactivators formed in the hemophilia A plasma, whereas the two-stageassay measures the procoagulant activity of preactivated factor VIII. Inthe two-stage assay, samples containing factor VIII that had beenreacted with thrombin were added to a mixture of activated partialthromboplastin and human hemophilia A plasma that had been preincubatedfor 5 min at 37° C. The resulting clotting times were then converted tounits/ml, based on the same human standard curve described above. Therelative activity in the two-stage assay was higher than in theone-stage assay because the factor VIII had been preactivated.

EXAMPLE 2 Characterization of the Functional Difference Between Humanand Porcine Factor VIII

The isolation of porcine and human plasma-derived factor VIII and humanrecombinant factor VIII have been described in the literature inFulcher, C. A. et al. (1982) Proc. Natl. Acad. Sci. USA 79:1648–1652;Toole et al. (1984) Nature 312:342–347 (Genetics Institute); Gitschieret al. (1984)Nature 312:326–330 (Genentech); Wood et al. (1984) Nature312:330–337 (Genentech); Vehar et al. 312 Nature 312:337–342(Genentech); Fass et al. (1982) Blood 59:594; Toole et al. (1986) Proc.Natl. Acad. Sci. USA 83:5939–5942. This can be accomplished in severalways. All these preparations are similar in subunit composition,although there is a functional difference in stability between human andporcine factor VIII.

For comparison of human recombinant and porcine factor VIII,preparations of highly-purified human recombinant factor VIII (CutterLaboratories, Berkeley, Calif.) and porcine factor VIII [immunopurifiedas described in Fass et al. (1982) Blood 59:594] were subjected tohigh-pressure liquid chromatography (HPLC) over a Mono Q™(Pharmacia-LKB, Piscataway, N.J.) anion-exchange column (Pharmacia,Inc.). The purposes of the Mono Q™ HPLC step were elimination of minorimpurities of exchange of human and porcine factor VIII into a commonbuffer for comparative purposes. Vials containing 1000–2000 units offactor VIII were reconstituted with 5 ml H₂O. Hepes (2 M at pH 7.4) wasthen added to a final concentration of 0.02 M. Factor VIII was appliedto a Mono Q™ HR 5/5 column equilibrated in 0.15 M NaCl, 0.02 M Hepes, 5mM CaCl₂, at pH 7.4 (Buffer A plus 0.15 M NaCl); washed with 10 mlBuffer A+0.15 M NaCl; and eluted with a 20 ml linear gradient, 0.15 M to0.90 M NaCl in Buffer A at a flow rate of 1 ml/min.

For comparison of human plasma-derived factor VIII (purified by Mono Q™HPLC) and porcine factor VIII, immunoaffinity-purified, plasma-derivedporcine factor VIII was diluted 1:4 with 0.04 M Hepes, 5 mM CaCl₂, 0.01%Tween-80, at pH 7.4, and subjected to Mono Q™ HPLC under the sameconditions described in the previous paragraph for human factor VIII.These procedures for the isolation of human and porcine factor VIII arestandard for those skilled in the art.

Column fractions were assayed for factor VIII activity by a one-stagecoagulation assay. The average results of the assays, expressed in unitsof activity per A₂₈₀ of material, are given in Table II, and indicatethat porcine factor VIII has at least six times greater activity thanhuman factor VIII when the one-stage assay is used.

TABLE II COMPARISON OF HUMAN AND PORCINE FACTOR VIII COAGULANT ACTIVITYActivity (U/A₂₈₀) Porcine 21,300 Human plasma-derived 3,600 Humanrecombinant 2,400

EXAMPLE 3 Comparison of the Stability of Human and Porcine Factor VIII

The results of the one-stage assay for factor VIII reflect activation offactor VIII to factor VIIIa in the sample and possibly loss of formedfactor VIIIa activity. A direct comparison of the stability of human andporcine factor VIII was made. Samples from Mono Q™ HPLC (Pharmacia,Inc., Piscataway, N.J.) were diluted to the same concentration andbuffer composition and reacted with thrombin. At various times, sampleswere removed for two-stage coagulation assay. Typically, peak activity(at 2 min) was 10-fold greater for porcine than human factor VIIIa, andthe activities of both porcine and human factor VIIIa subsequentlydecreased, with human factor VIIIa activity decreasing more rapidly.

Generally, attempts to isolate stable human factor VIIIa are notsuccessful even when conditions that produce stable porcine factor VIIIaare used. To demonstrate this, Mono Q™ HPLC-purified human factor VIIIwas activated with thrombin and subjected to Mono S™ cation-exchange(Pharmacia, Inc.) HPLC under conditions that produce stable porcinefactor VIIIa, as described by Lollar et al. (1989) Biochemistry 28:666.

Human factor VIII, 43 μg/ml (0.2 μM) in 0.2 M NaCl, 0.01 M Hepes, 2.5 mMCaCl₂, at pH 7.4, in 10 ml total volume, was reacted with thrombin(0.036 μM) for 10 min, at which time FPR-CH₂ClD-phenyl-prolyl-arginyl-chloromethyl ketone was added to a concentrationof 0.2 μM for irreversible inactivation of thrombin. The mixture thenwas diluted 1:1 with 40 mM 2-(N-morpholino) ethane sulfonic acid (MES),5 mM CaCl₂, at pH 6.0, and loaded at 2 ml/min onto a Mono S™ HR 5/5 HPLCcolumn (Pharmacia, Inc.) equilibrated in 5 mM MES, 5 mM CaCl₂, at pH 6.0(Buffer B) plus 0.1 M NaCl. Factor VIIIa was eluted without columnwashing with a 20 ml gradient from 0.1 M NaCl to 0.9 M NaCl in Buffer Bat 1 ml/min.

The fraction with coagulant activity in the two-stage assay eluted as asingle peak under these conditions. The specific activity of the peakfraction was approximately 7,500 U/A₂₈₀. Sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the Mono S™factor VIIIa peak, followed by silver staining of the protein, revealedtwo bands corresponding to a heterodimeric (A3-C1–C2/A1) derivative offactor VIII. Although the A2 fragment was not identified by silverstaining under these conditions because of its low concentration, it wasidentified as a trace constituent by ¹²⁵I-labeling.

In contrast to the results with human factor VIII, porcine factor VIIIaisolated by Mono S™ HPLC under the same conditions had a specificactivity 1.6×10⁶ U/A₂₈₀. Analysis of porcine factor VIIIa by SDS-PAGErevealed 3 fragments corresponding to A1, A2, and A3-C1–C2 subunits,demonstrating that porcine factor VIIIa possesses three subunits.

The results of Mono S™ HPLC of human thrombin-activated factor VIIIpreparations at pH 6.0 indicate that human factor VIIIa is labile underconditions that yield stable porcine factor VIIIa. However, althoughtrace amounts of A2 fragment were identified in the peak fraction,determination of whether the coagulant activity resulted from smallamounts of heterotrimeric factor VIIIa or from heterodimeric factorVIIIa that has a low specific activity was not possible from this methodalone.

Away to isolate human factor VIIIa before it loses its A2 subunit isdesirable to resolve this question. To this end, isolation wasaccomplished in a procedure that involves reduction of the pH of theMono S™ buffers to pH 5. Mono Q™-purified human factor VIII (0.5 mg) wasdiluted with H₂O to give a final composition of 0.25 mg/ml (1 μm) factorVIII in 0.25 M NaCl, 0.01 M Hepes, 2.5 mM CaCl₂, 0.005% Tween-80, at pH7.4 (total volume 7.0 ml). Thrombin was added to a final concentrationof 0.072 μm and allowed to react for 3 min. Thrombin was theninactivated with FPR-CH₂Cl (0.2 μm). The mixture then was diluted 1:1with 40 mM sodium acetate, 5 mM CaCl₂, 0.01% Tween-80, at pH 5.0, andloaded at 2 ml/min onto a Mono S™ HR 5/5 HPLC column equilibrated in0.01 M sodium acetate, 5 mM CaCl₂, 0.01% Tween-80, at pH 5.0, plus 0.1 MNaCl. Factor VIIIa was eluted without column washing with a 20 mlgradient from 0.1 M NaCl to 1.0 M NaCl in the same buffer at 1 ml/min.This resulted in recovery of coagulant activity in a peak that containeddetectable amounts of the A2 fragment as shown by SDS-PAGE and silverstaining. The specific activity of the peak fraction was tenfold greaterthan that recovered at pH 6.0 (75,000 U/A₂₈₀ v.7,500 U/A₂₈₀). However,in contrast to porcine factor VIIIa isolated at pH 6.0, which isindefinitely stable at 4° C., human factor VIIIa activity decreasedsteadily over a period of several hours after elution from Mono S™.Additionally, the specific activity of factor VIIIa purified at pH 5.0and assayed immediately is only 5% that of porcine factor VIIIa,indicating that substantial dissociation occurred prior to assay.

These results demonstrate that both human and porcine factor VIIIa arecomposed of three subunits (A1, A2, and A3-C1–C2). Dissociation of theA2 subunit is responsible for the loss of activity of both human andporcine factor VIIIa under certain conditions, such as physiologicalionic strength, pH, and concentration. The relative stability of porcinefactor VIIIa under certain conditions is because of stronger associationof the A2 subunit.

EXAMPLE 4 Preparation of Hybrid Human/Porcine Factor VIII byReconstitution with Subunits

Porcine factor VIII light chains and factor VIII heavy chains wereisolated as follows. A 0.5 M solution of EDTA at pH 7.4 was added toMono Q™-purified porcine factor VIII to a final concentration of 0.05 Mand was allowed to stand at room temperature for 18–24 h. An equalvolume of 10 mM histidine-C1, 10 mM EDTA, 0.2% v/v Tween 80, at pH 6.0(Buffer B), was added, and the solution was applied at 1 ml/min to aMono S™ HR 5/5 column previously equilibrated in Buffer A plus 0.25 MNaCl. Factor VIII heavy chains did not bind the resin, as judged bySDS-PAGE. Factor VIII light chain was eluted with a linear, 20 ml,0.1–0.7 M NaCl gradient in Buffer A at 1 ml/min and was homogeneous bySDS-PAGE. Factor VIII heavy chains were isolated by mono Q™ HPLC(Pharmacia, Inc., Piscataway, N.J.) in the following way. Factor VIIIheavy chains do not adsorb to mono S™ during the purification of factorVIII light chains. The fall-through material that contained factor VIIIheavy chains was adjusted to pH 7.2 by addition of 0.5 M Hepes buffer,pH 7.4, and applied to a mono Q™ HR5/5 HPLC column (Pharmacia, Inc.)equilibrated in 0.1 M NaCl, 0.02 M Hepes, 0.01% Tween-80, pH 7.4. Thecolumn was washed with 10 ml of this buffer, and factor VIII heavychains were eluted with a 20 ml 0.1–1.0 M NaCl gradient in this buffer.Human light chains and heavy chains were isolated in the same manner.

Human and porcine light and heavy chains were reconstituted according tothe following steps. Ten μl human or porcine factor VIII light chain,100 μg/ml, was mixed in 1 M NaCl, 0.02 M Hepes, 5 mM CaCl₂, 0.01%Tween-80, pH 7.4, with (1) 25 μl heterologous heavy chain, 60 μg/ml, inthe same buffer; (2) 10 μl 0.02 M Hepes, 0.01% Tween-80, pH 7.4; (3) 5μl 0.6 M CaCl₂, for 14 hr at room temperature. The mixture was diluted ¼with 0.02 M MES, 0.01% Tween-80, 5 mM CaCl₂, pH 6 and applied to Mono S™Hr5/5 equilibrated in 0.1 M NaCl, 0.02 M MES, 0.01% Tween-80, 5 mMCacl₂, pH 6.0. A 20 ml gradient was run from 0.1–1.0 M NaCl in the samebuffer at 1 ml/min, and 0.5 ml fractions were collected. Absorbance wasread at 280 nm of fractions, and fractions were assayed with absorbancefor factor VIII activity by the one-stage clotting assay. Heavy chainswere present in excess, because free light chain (not associated withheavy chain) also binds Mono S™; excess heavy chains ensure that freelight chains are not part of the preparation. Reconstitution experimentsfollowed by Mono S™ HPLC purification were performed with all fourpossible combinations of chains: human light chain/human heavy chain,human light chain/porcine heavy chain, porcine light chain/porcine heavychain, porocine light chain/human heavy chain. Table III shows thathuman light chain/porcine heavy chain factor VIII has activitycomparable to native porcine factor VIII (Table II), indicating thatstructural elements in the porcine heavy chain are responsible for theincreased coagulant activity of porcine factor VIII compared to humanfactor VIII.

TABLE III COMPARISON OF HYBRID HUMAN/PORCINE FACTOR VIII COAGULANTACTIVITY WITH HUMAN AND PORCINE FACTOR VIII Activity (U/A₂₈₀) Porcinelight chain/porcine heavy chain 30,600 Human light chain/porcine heavychain 44,100 Porcine light chain/human heavy chain 1,100 Human lightchain/human heavy chain 1,000

EXAMPLE 5 Preparation of Active Hybrid Human/Porcine Factor VIII byReconstitution with Domains

The porcine A1/A3–C1–C2 dimer, the porcine A2 domain, the humanA1/A3-C1–C2 dimer, and the human A2 domain were each isolated fromporcine or human blood, according to the method described in Lollar etal. (1992) J. Biol. Chem. 267(33):23652–23657. For example, to isolatethe porcine A1/A3-C1–C2 dimer, porcine factor VIIIa (140 μg) at pH 6.0was raised to pH 8.0 by addition of 5 N NaOH for 30 minutes, producingdissociation of the A2 domain and 95 percent inactivation by clottingassay. The mixture was diluted 1:8 with buffer B (20 mM HEPES, 5 mMCaCl₂, 0.01% Tween-80, pH 7.4) and applied to a monoS columnequilibrated in buffer B. The A1/A3-C1–C2 dimer eluted as a single sharppeak at approximately 0.4 M NaCl by using a 0.1–1.0 M NaCl gradient inbuffer B. To isolate the porcine A2 domain, porcine factor VIIIa wasmade according to the method of Lollar et al. (1989) Biochem 28:666–674,starting with 0.64 mg of factor VIII. Free porcine A2 domain wasisolated as a minor component (50 μg) at 0.3 M NaCl in the MonoS™chromatogram.

Hybrid human/porcine factor VIII molecules were reconstituted from thedimers and domains as follows. The concentrations and buffer conditionsfor the purified components were as follows: porcine A2, 0.63 μM inbuffer A (5 mM MES; 5 mM CaCl₂, 0.01% Tween 80, pH 6.0) plus 0.3 M NaCl;porcine A1/A3-C1–C2, 0.27 μM in buffer B plus 0.4 M NaCl, pH 7.4; humanA2, 1 μM in 0.3 M NaCl, 10 mM histidine-HCl, 5 mM CaCl₂, 0.01% Tween 20,pH 6.0; human A1/A3-C1–C2,0.18 μM in 0.5 M NaCl, 10 mM histidine-Cl, 2.5mM CaCl₂, 0.1% Tween-20, pH 6.0. Reconstitution experiments were done bymixing equal volumes of A2 domain and A1/A3-C1–C2 dimer. In mixingexperiments with porcine A1/A3-C1–C2 dimer, the pH was lowered to 6.0 byaddition of 0.5 M MES, pH 6.0, to 70 mM.

The coagulation activities of all four possible hybrid factor VIIIamolecules—[pA2/(hA1/A3-C1–C2)], [hA2/(pA1/A3-C1–C2)],[pA2/(pA1/pA3-C1–C2)], and [hA2/(hA1/A3-C1–C2)]—were obtained by atwo-stage clotting assay at various times.

The generation of activity following mixing the A2 domains andA1/A3-C1–C2 dimers was nearly complete by one hour and was stable for atleast 24 hours at 37° C. Table IV shows the activity of reconstitutedhybrid factor VIIIa molecules when assayed at 1 hour. The two-stageassay, by which the specific activities of factor VIIIa molecules wereobtained, differs from the one-stage assay, and the values cannot becompared to activity values of factor VIII molecules obtained by aone-stage assay.

TABLE IV COMPARISON OF COAGULANT ACTIVITIES OF DOMAIN- SUBSTITUTEDHYBRID HUMAN/PORCINE FACTOR VIIIa Specific Hybrid fVIIIa Activity (U/mg)Porcine A2 + Human 140,000 A1/A3-C1-C2 Porcine A2 + Porcine 70,000A1/A3-C1-C2 Human A2 + Porcine 40,000 A1/A3-C1-C2 Human A2 + Human40,000 A1/A3-C1-C2

Table IV shows that the greatest activity was exhibited by the porcineA2 domain/human A1/A3-C1–C2 dimer, followed by the porcine A2domain/porcine A1/A3-C1–C2 dimer.

Thus, when the A2 domain of porcine factor VIIIa was mixed with theA1/A3-C1–C2 dimer of human factor VIIIa, coagulant activity wasobtained. Further, when the A2 domain of human factor VIIIa was mixedwith the A1/A3-C1–C2 dimer of porcine factor VIIIa, coagulant activitywas obtained. By themselves, the A2, A1, and A3-C1–C2 regions have nocoagulant activity.

EXAMPLE 6 Isolation and Sequencing of the A2 Domain of Porcine FactorVIII

Only the nucleotide sequence encoding the B domain and part of the A2domain of porcine factor VIII has been sequenced previously [Toole etal. (1986) Proc. Natl. Acad. Sci. USA 83:5939–5942]. The cDNA andpredicted amino acid sequences (SEQ ID NOs: 3 and 4, respectively) forthe entire porcine factor VIII A2 domain are disclosed herein.

The porcine factor VIII A2 domain was cloned by reverse transcription ofporcine spleen total RNA and PCR amplification; degenerate primers basedon the known human factor VIII cDNA sequence and an exact porcine primerbased on a part of the porcine factor VIII sequence were used. A 1 kbPCR product was isolated and amplified by insertion into a Bluescript™(Stratagene) phagemid vector.

The porcine A2 domain was completely sequenced by dideoxy sequencing.The cDNA and predicted amino acid sequences are as described in SEQ IDNOs: 3 and 4, respectively.

EXAMPLE 7 Preparation of Recombinant Hybrid Human/Animal Factor VIII

The nucleotide and predicted amino acid sequences (SEQ ID NOs: 1 and 2,respectively) of human factor VIII have been described in the literature[Toole et al. (1984) Nature 312:342–347 (Genetics Institute); Gitschieret al. Nature 312:326–330 (Genentech); Wood, et al. (1984) Nature312:330–337 (Genentech); Vehar et al. Nature 312:337–342 (Genentech)].

Making recombinant hybrid human/animal factor VIII requires that aregion of human factor VIII cDNA (Biogen Corp.) be removed and theanimal cDNA sequence having sequence identity be inserted. Subsequently,the hybrid cDNA is expressed in an appropriate expression system. As anexample, hybrid factor VIII cDNAs were cloned in which some or all ofthe porcine A2 domain was substituted for the corresponding human A2sequences. Initially, the entire cDNA sequence corresponding to the A2domain of human factor VIII and then a smaller part of the A2 domain waslooped out by oligonucleotide-mediated mutagenesis, a method commonlyknown to those skilled in the art (see, e.g., Sambrook, J., E. F.Fritsch, and T. Maniatis, Molecular Cloning: A Laboratory Manual,Chapter 15, Cold Spring Harbor Press, Cold Spring Harbor, 1989). Thesteps were as follows.

Materials.

Methoxycarbonyl-D-cyclohexylglycyl-glycl-arginine-p-nitroanilide(Spectrozyme™ Xa) and anti-factor VIII monoclonal antibodies ESH4 andESH8 were purchased from American Diagnostica (Greenwich, Conn.).Unilamellar phosphatidylcholine/phosphatidylserine (75/25, w/w) vesicleswere prepared according to the method of Barenholtz, Y., et al., 16Biochemistry 2806–2810 (1977)). Recombinant desulfatohirudin wasobtained from Dr. R. B. Wallis, Ciba-Geigy Pharmaceuticals (Cerritos,Calif.). Porcine factors IXa, X, Xa, and thrombin were isolatedaccording to the methods of Lollar et al. (1984) Blood 63:1303–1306, andDuffy, E. J. et al. (1992) J. Biol. Chem. 207:7621–7827. Albumin-freepure recombinant human factor VIII was obtained from Baxter-Biotech(Deerfield, Ill.).

Cloning of the Porcine Factor VIII A2 Domain.

The cDNA encoding the porcine A2 domain was obtained following PCR ofreverse-transcribed porcine spleen mRNA isolated as described byChomczyneki et al. (1987) Anal. Biochem. 162:156–159. cDNA was preparedusing the first-strand cDNA synthesis kit with random hexamers asprimers (Pharmacia, Piscataway, N.J.). PCR was carried out using a5′-terminal degenerate primer 5′ AARCAYCCNAARACNTGGG 3′ (SEQ ID NO:11),based on known limited porcine A2 amino acid sequence, and a 3′-terminalexact primer, 5′ GCTCGCACTAGGGGGTCTTGAATTC 3′ (SEQ ID NO:12), based onknown porcine DNA sequence immediately 3′ of the porcine A2 domain.These oligonucleotides correspond to nucleotides 1186–1203 and 2289–2313in the human sequence (SEQ ID NO:1). Amplification was carried out for35 cycles (1 minute 94° C., 2 minutes 50° C., 2 minutes 72° C.) usingTaq DNA polymerase (Promega Corp., Madison, Wis.). The 1.1-kilobaseamplified fragment was cloned into pBluescript II KS-(Stratagene) at theEcoRV site using the T-vector procedure, as described by Murchuk, D. etal. (1991) Nucl. Acids Res. 19:1154. Escherichia coli XL1-Blue-competentcells were transformed, and plasmid DNA was isolated. Sequencing wascarried out in both directions using Sequenase™ version 2.0 (U.S.Biochemical Corp., a Division of Amersham LifeScience, Inc., ArlingtonHts, Ill.). This sequence was confirmed by an identical sequence thatwas obtained by direct sequencing of the PCR product from an independentreverse transcription of spleen RNA from the same pig (CircumVent™, NewEngland Biolabs, Beverly, Mass.). The region containing the epitope forautoantibody RC was identified as 373–536 in human factor VIII (SEQ IDNO:2).

Construction and Expression of a Hybrid Human/Porcine Factor VIII cDNA.

B-domainless human factor VIII (HB⁻, from Biogen, Inc. Cambridge,Mass.), which lacks sequences encoding for amino acid residues 741–1648(SEQ ID NO:2), was used as the starting material for construction of ahybrid human/porcine factor VIII. HB⁻ was cloned into the expressionvector ReNeo. To facilitate manipulation, the cDNA for factor VIII wasisolated as a XhoI/HpaI fragment from ReNeo and cloned into XhoI/EcoRVdigested pBlueScript II KS. An oligonucleotide, 5′CCTTCCTTTATCCAAATACGTAGATCAAGAGGAAATTGAC 3′ (SEQ ID NO:7), was used in asite-directed mutagenesis reaction using uracil-containing phage DNA, asdescribed by Kunkel, T. A. et al. (1991) Meth. Enzymol 204:125–139, tosimultaneously loop-out the human A2 sequence (nucleotides 1169–2304 inSEQ ID NO:1) and introduce a SnaBI restriction site. The A2-domainlesshuman factor VIII containing plasmid was digested with SnaBI followed byaddition of ClaI linkers. The porcine A2 domain was then amplified byPCR using the phosphorylated 5′ primer 5′ GTAGCGTTGCCAAGAAGCACCCTAAGACG3′ (SEQ ID NO:8) and 3′ primer 5′ GAAGAGTAGTACGAGTTATTTCTCTGGGTTCAATGAC3′ (SEQ ID NO:9), respectively. ClaI linkers were added to the PCRproduct followed by ligation into the human factor VIII-containingvector. The A1/A2 and A2/A3 junctions were corrected to restore theprecise thrombin cleavage and flanking sequences by site-directedmutagenesis using the oligonucleotide shown in SEQ ID NO:8 andnucleotides 1–22 (5′ GAA . . . TTC in SEQ ID NO:9) to correct the 5′-and 3′- terminal junctions, respectively. In the resulting construct,designated HP1, the human A2 domain was exactly substituted with theporcine A2 domain. A preliminary product contained an unwanted thymineat the A1–A2 junction as a result of the PCR amplification of theporcine A2 domain. This single base was looped out by use of themutagenic oligonucleotide 5′ CCTTTATCCAAATACGTAGCGTTTGCCAAGAAG 3′ (SEQID NO:10). The resulting hybrid nucleotide sequence encoded activefactor VIII having human A1, porcine A2 and human A3, C1 and C2 domains.

A region containing 63% of the porcine NH₂-terminal A2 domain, whichencompasses the putative A2 epitope, was substituted for the homologoushuman sequence of B-domainless cDNA by exchanging SpeI/BamHI fragmentsbetween the pBluescript plasmids containing human factor VIII andhuman/porcine A2 factor VIII cDNA. The sequence was confirmed bysequencing the A2 domain and splice sites. Finally, a Spel/Apalfragment, containing the entire A2 sequence, was substituted in place ofthe corresponding sequence in HB⁻, producing the HP2 construct.

Preliminary expression of HB⁻ and HP2 in COS-7 cells was tested afterDEAE-dextran-mediated DNA transfection, as described by Seldon, R. F.,in Current Protocols in Molecular Biology (Ausubel, F. M., et al., eds),pp. 9.21–9.26, Wiley Interscience, N.Y. After active factor VIIIexpression was confirmed and preliminary antibody inhibition studieswere done, HB⁻ and HP2 DNA were then stably transfected into babyhamster kidney cells using liposome-mediated transfection (Lipofectin®Life Technologies, Inc., Gaithersburg, Md.). Plasmid-containing cloneswere selected for G418 resistance in Dulbecco's modified Eagle'smedium-F12, 10% fetal calf serum (DMEM-F12/10% fetal calf serum)containing 400 μg/ml G418, followed by maintenance in DMEM-F12/10% fetalcalf serum containing 100 μg/ml G418. Colonies showing maximumexpression of HB⁻ and HP2 factor VIII activity were selected by ringcloning and expanded for further characterization.

HB⁻ and HP2 factor VIII expression was compared by plasma-free factorVIII assay, one-stage clotting assay, and enzyme-linked immunosorbentassay using purified recombinant human factor VIII as a standard.Specific coagulant activities of 2600 and 2580 units/mg were obtainedfor HB⁻ and HP2, respectively. HB⁻ and HP2 produced 1.2 and 1.4units/ml/48 hours/10⁷ cells, respectively. This is identical to that ofthe wild type construct (2,600±200 units/mg). The specific activities ofHB⁻ and HP2 were indistinguishable in the plasma-free factor VIII assay.

The biological activity of recombinant hybrid human/animal andequivalent factor VIII with A1, A2, A3, C1, and/or C2 domainsubstitutions can be evaluated initially by use of a COS-cell mammaliantransient expression system. Hybrid human/animal and equivalent cDNA canbe transfected into COS cells, and supernatants can be analyzed forfactor VIII activity by use of one-stage and two-stage coagulationassays as described above. Additionally, factor VIII activity can bemeasured by use of a chromogenic substrate assay, which is moresensitive and allows analysis of larger numbers of samples. Similarassays are standard in the assay of factor VIII activity [Wood et al.(1984) Nature 312:330–337; Toole et al. (1984) Nature 312:342–347].Expression of recombinant factor VIII in COS cells is also a standardprocedure [Toole et al. (1984) Nature 312:342–347; Pittman et al. (1988)Proc. Natl. Acad. Sci. USA 85:2429–2433].

The human factor VIII cDNA used as starting materials for therecombinant molecules described herein has been expressed in COS cellsyielding a product with biological activity. This material, as describedabove, can be used as a standard to compare hybrid human/animal factorVIII molecules. The activity in the assays is converted to a specificactivity for proper comparison of the hybrid molecules. For this, ameasurement of the mass of factor VIII produced by the cells isnecessary and can be done by immunoassay with purified human and/oranimal factor VIII as standards. Immunoassays for factor VIII areroutine for those skilled in the art [See, e.g., Lollar et al. (1988)Blood 71:137–143].

EXAMPLE 8 Determination of Inhibitory Activity in Hybrid Human/Animaland Equivalent Factor VIII

Sequences of human and animal factor VIII likely to be involved asepitopes (i.e., as recognition sites for inhibitory antibodies thatreact with factor VIII) can be determined using routine procedures, forexample through use of assay with antibodies to factor VIII combinedwith site directed mutagenesis techniques such as splicing by overlapextension methods (SOE), as shown below. Sequences of animal factor VIIIthat are not antigenic compared to corresponding antigenic humansequences can be identified, and substitutions can be made to insertanimal sequences and delete human sequences according to standardrecombinant DNA methods. Sequences of amino acids such as alanineresidues having no known sequence identity to factor VIII can also besubstituted by standard recombinant DNA methods or by alanine scanningmutagenesis. Porcine factor VIII reacts less than human factor VIII withsome inhibitory antibodies; this provides a basis for current therapyfor patients with inhibitors. After the recombinant hybrids are made,they can be tested in vitro for reactivity with routine assays,including the Bethesda inhibitor assay. Those constructs that are lessreactive than native human factor VIII and native animal factor VIII arecandidates for replacement therapy.

The epitopes to which most, if not all, inhibitory antibodies reactivewith human factor VIII are directed are thought to reside in two regionsin the 2332 amino acid human factor VIII molecule, the A2 domain (aminoacid residues 373–740) and the C2 domain (amino acid residues 2173–2332,both sequences shown in SEQ ID NO:2). The A2 epitope has been eliminatedby making a recombinant hybrid human-porcine factor VIII molecule inwhich part of the human A2 domain is replaced by the porcine sequencehaving sequence identity to the replaced human amino acid sequence. Thiswas accomplished, as described in example 7, by cloning the porcine A2domain by standard molecular biology techniques and then cutting andsplicing within the A2 domain using restriction sites. In the resultingconstruct, designated HP2, residues 373–604 (SEQ ID NO:4) of porcinefactor VIII were substituted into the human A2 domain. HP2 was assayedfor immunoreactivity with anti-human factor VIII antibodies using thefollowing methods.

Factor VIII Enzyme-linked Immunosorbent Assay.

Microtiter plate wells were coated with 0.15 ml of 6 μg/ml ESH4, a humanfactor VIII light-chain antibody, and incubated overnight. After theplate was washed three times with H₂O, the wells were blocked for 1 hourwith 0.15 M NaCl, 10 mM sodium phosphate, 0.05% Tween 20, 0.05% nonfatdry milk, 0.05% sodium azide, pH 7.4. To increase sensitivity, samplescontaining factor VIII were activated with 30 nM thrombin for 15minutes. Recombinant desulfatohirudin then was added at 100 nM toinhibit thrombin. The plate was washed again and 0.1 ml of sample orpure recombinant human factor VIII (10–600 ng/ml), used as the standard,were added. Following a 2 hour incubation, the plate was washed and 0.1ml of biotinylated ESH8, another factor VIII light-chain antibody, wasadded to each well. ESH8 was biotinylated using the Piercesulfosuccinimidyl-6-(biotinamide)hexanoate biotinylation kit. After a 1hour incubation, the plate was washed and 0.1 ml of strepavidin alkalinephosphatase was added to each well. The plate was developed using theBio-Rad alkaline phosphatase substrate reagent kit, and the resultingabsorbance at 405 nm for each well was determined by using a Vmaxmicrotiter plate reader (Molecular Devices, Inc., Sunnyville, Calif.).Unknown factor VIII concentrations were determined from the linearportion of the factor VIII standard curve.

Factor VIII Assays.

HB⁻ and HP2 factor VIII were measured in a one-stage clotting assay,which was performed as described above [Bowie, E. J. W., and C. A. Owen,in Disorders of Hemostasis (Ratnoff and Forbes, eds) pp. 43–72, Grunn &Stratton, Inc., Orlando, Fla. (1984)], or by a plasma-free assay asfollows. HB⁻ or HP2 factor VIII was activated by 40 nM thrombin in 0.15M NaCl, 20 nM HEPES, 5 mM CaCl₂, 0.01% Tween 80, pH 7.4, in the presenceof 10 nM factor IXa, 425 nM factor X, and 50 μM unilamellarphosphatidylserine/phosphatidylcholine (25/75, w/w) vesicles. After 5minutes, the reaction was stopped with 0.05 M EDTA and 100 nMrecombinant desulfatohirudin, and the resultant factor Xa was measuredby chromogenic substrate assay, according to the method of Hill-Eubankset al (1990) J. Biol. Chem. 265:17854–17858. Under these conditions, theamount of factor Xa formed was linearly proportional to the startingfactor VIII concentration as judged by using purified recombinant humanfactor VIII (Baxter Biotech, Deerfield, Ill.) as the standard.

Prior to clotting assay, HB⁻ or HP2 factor VIII were concentrated from48 hour conditioned medium to 10–15 units/ml by heparin-Sepharose™chromatography. HB⁻ or HP2 factor VIII were added to hemophilia A plasma(George King Biomedical) to a final concentration of 1 unit/ml.Inhibitor titers in RC or MR plasma or a stock solution of mAb 413 IgG(4 μM) were measured by the Bethesda assay as described by Kasper, C. K.et al. (1975) Thromb. Diath. Haemorrh 34:869–872. Inhibitor IgG wasprepared as described by Leyte, A. et al. (1991) J. Biol. Chem.266:740–746.

HP2 does not react with anti-A2 antibodies. Therefore, residues 373–603must contain an epitope for anti-A2 antibodies.

Preparation of Hybrid Human-porcine Factor VIII and Assay by Splicing byOverlap Extension (SOE).

Several more procoagulant recombinant hybrid human/porcine factor VIIIB-domainless molecules with porcine amino acid substitutions in thehuman A2 region have been prepared to further narrow the A2 epitope.Besides restriction site techniques, the “splicing by overlap extension”method (SOE) as described by Ho et al. (1989) Gene 77:51–59, has beenused to substitute any arbitrary region of porcine factor VIII cDNA. InSOE, the splice site is defined by overlapping oligonucleotides that canbe amplified to produce the desired cDNA by PCR. Ten cDNA constructs,designated HP4 through HP13, have been made. They were inserted into theReNeo expression vector, stably transfected into baby hamster kidneycells, and expressed to high levels [0.5–1 μg (approximately 3–6units)/10⁷ cells/24 hours] as described in Example 7. Factor VIIIcoagulant activity was determined in the presence and absence of a modelmurine monoclonal inhibitory antibody specific for the A2 domain,mAb413. In the absence of inhibitor, all of the constructs had aspecific coagulant activity that was indistinguishable from B(−) humanfactor VIII.

The hybrid human/porcine factor VIII constructs were assayed forreactivity with the anti-A2 inhibitor mAb413 using the Bethesda assay[Kasper et al. (1975) Thromb. Diath. Haemorrh. 34:869–872]. The Bethesdaunit (BU) is the standard method for measuring inhibitor titers. Theresults are shown in Table V, and are compared to recombinant humanfactor VIII.

TABLE V COMPARISON OF IMMUNOREACTIVITY OF AMINO ACID- SUBSTITUTED HYBRIDHUMAN/PORCINE FACTOR VIII Porcine Inhibition Construct SubstitutionmAb413(BU/mg IgG) Human B(−) fVIII None 1470 HP4 373–540 <0.7 HP5373–508 <0.7 HP6 373–444 1450 HP7 445–508 <0.7 HP8 373–483 1250 HP9484–508 <0.7 HP10 373–403 1170 HP11 404–508 <0.7 HP12 489–508 <0.7 HP13484–488 <0.7

The boundaries of porcine substitutions are defined by the first aminoacids that differ between human and porcine factor VIII at theNH₂-terminal and C-terminal ends of the insertion. As shown in Table V,if the Bethesda titer is not measurable (<0.7 BU/mg IgG), then an A2epitope lies in the region of substituted porcine sequence. The epitopehas been progressively narrowed to residues 484–509 (SEQ ID NO:2),consisting of only 25 residues, as exemplified by non-reactivity ofmAb413 with HP9. Among constructs HP4 through HP11, HP9 was the most“humanized” construct that did not react with the inhibitor. Thisindicates that a critical region in the A2 epitope is located within thesequence Arg484-IIe508.

Based on a comparison between human and porcine factor VIII of the aminoacid sequence in this critical region, two more constructs, HP12 andHP13, were made, in which corresponding porcine amino acid sequence wassubstituted for human amino acids 489–508 and 484–488, respectively.Neither reacts with mAb413. This indicates that residues on each side ofthe Arg488-Ser489 bond are important for reaction with A2 inhibitors. InHP12 only 5 residues are non-human, and in HP13 only 4 residues arenon-human. The 484–508, 484–488, and 489–508 porcine substituted hybridsdisplayed decreased inhibition by A2 inhibitors from four patientplasmas, suggesting that there is little variation in the structure ofthe A2 epitope according to the inhibitor population response.

The reactivity of the most humanized constructs, HP9, HP12, and HP13,with two anti-A2 IgG5 preparations prepared from inhibitor plasmas wasdetermined. Like mAb413, these antibodies did not react with HP9, HP12,and HP13, but did react with the control constructs HP(−) and HP8.

The region between 484–508 can be further analyzed for finalidentification of the critical A2 epitope, using the same procedures.

The methods described in Examples 7 and 8 can be used to prepare otherhybrid human/non-porcine mammalian factor VIII with amino acidsubstitution in the human A2 or other domains, hybrid human/animal oranimal/animal factor VIII with amino acid substitution in any domain, orhybrid factor VIII equivalent molecules or fragments of any of these,such hybrid factor VIII having reduced or absent immunoreactivity withanti-factor VIII antibodies.

EXAMPLE 9 Elimination of Human Factor VIII A2 Inhibitor Reactivity bySite-directed Mutagenesis

Example 8 showed that substitution of the porcine sequence bounded byresidues 484 and 508 into the human factor VIII A2 domain yields amolecule that has markedly decreased reactivity with a panel ofA2-specific factor VIII inhibitors [see also Healey et al. (1995) J.Biol. Chem. 270:14505–14509]. In this region, there are 9 amino aciddifferences between human and porcine factor VIII. These nine residuesin human B-domainless factor VIII, R484, P485, Y487, P488, R489, P492,V495, F501, and I508 (using the single letter amino code), wereindividually changed to alanine by site-directed mutagenesis.Additionally, Mlu1 and Sac2 restriction sites were placed in the factorVIII cDNA at sites 5′ and 3′ relative to the A2 epitope, withoutchanging the amino acids corresponding to these sites, to facilitatecloning. The nine mutants were stably transfected into baby hamsterkidney cells and expressed to high levels. All nine producedbiologically active factor VIII. They were partially purified andconcentrated by heparin-Sepharose chromatography as described by Healeyet al.

The mutants have been characterized by their reactivity with the murinemonoclonal inhibitor MAb413 as in Example 7. This inhibitor recognizesthe same or a very closely clustered epitope in the A2 domain as allhuman inhibitors studied to date. Inhibitor reactivity was measuredusing the Bethesda assay. Briefly, the Bethesda titer of an inhibitor isthe dilution of inhibitor that inhibits factor VIII by 50% in a standardone-stage factor VIII clotting assay. For example, if solution ofantibody is diluted 1/420 and it inhibits the recombinant factor VIIItest sample by 50%, the Bethesda titer is 420 U. In the case of a puremonoclonal like MAb413, the mass of antibody is known, so the resultsare expressed in Bethesda units (BU) per mg MAb413. To find the 50%inhibition point, a range of dilutions of MAb413 was made and 50%inhibition was found by a curve fitting procedure. The results are asfollows:

TABLE VI Mutation MAb413 titer (BU/mg) % Reactivity* Wild-type, B(−)fVII9400 — 484 → A 160 1.7 P485 → A 4000 42 Y487 → A 50 0.53 P488 → A 350037 R489 → A 1.6 0.015 R490 → A <—> <0.2> P492 → A 630 6.7 V495 → A 10700113 F501 → A 11900 126 I508 → A 5620 60 *Relative to wild-type

These results indicate that it is possible to reduce the antigenicity offactor VIII toward the model A2 inhibitor by over a factor of 10 bymaking alanine substitutions at positions 484, 487, 489, and 492. Thereactivity of R489→A is reduced by nearly 4 orders of magnitude. Any ofthese alanine substitutions can be therapeutically useful to reduce theantigenicity and the immunogenicity of factor VIII.

The results confirm the efficacy of alanine-scanning mutagenesis andfurther demonstrate that biological activity is retained even though theamino acid sequence has been altered within an epitope reactive to aninhibitory antibody. Five of the nine sites where the human and porcinesequences differ are also sites where the human and murine sequencesdiffer. The factor VIIIs having alanine substitutions at these positionsare therefore examples of a hybrid factor VIII equivalent moleculehaving a sequence with no known sequence identify with any presentlyknown mammalian factor VIII.

Further modification, e.g. by combining two alanine substitutions, canalso provide greatly reduced antigenicity for a wider range of patients,since polyclonal variant antibodies differing from patient to patientcan react with variants of the factor VIII A2 epitope. In addition,immunogenicity (the capacity to induce antibodies) is further reduced byincorporation of more than one amino acid substitution. Suchsubstitutions can include both alanine, porcine-specific amino acids, orother amino acids known to have low immunogenic potential. Thesubstitutions at positions 490, 495 and 501 are likely to be useful inreducing immunogenicity. In addition, these substitutions are likely toreduce reactivity to certain patient antibodies.

Other effective, antigenicity-reducing amino acid substitutions, besidesalanine, can be made as long as care is taken to avoid those previouslynoted as being major contributors to antigen-antibody binding energy, orhaving bulky or charged side chains. Amino acids whose substitutionswithin an epitope reduce the antigenic reactivity thereof are termed“immunoreactivity-reducing” amino acids herein. Besides alanine, otherimmunoreactivity-reducing amino acids include, without limitation,methionine, leucine, serine and glycine. It will be understood that thereduction of immunoreactivity achievable by a given amino acid will alsodepend on any effects the substitution may have on protein conformation,epitope accessibility and the like.

EXAMPLE 10

Klenow fragment, phosphorylated ClaI linkers, NotI linkers, T4 ligase,and Taq DNA polymerase were purchased from Promega (Madison, Wis.).Polynucleotide kinase was purchased from Life Technologies, Inc.,Gaithersburg, Md. γ³²P-ATP (Redivue, >5000 Ci/mmol) was purchased fromAmersham. pBluescript II KS- and E. coli Epicurean XL1-Blue cells werepurchased from Stratagene (La Jolla, Calif.). Synthetic oligonucleotideswere purchased from Life Technologies, Inc. or Cruachem, Inc.5′-phosphorylated primers were used when PCR products were produced forcloning purposes. Nucleotide (nt) numbering of oligonucleotides used asprimers for polymerase chain reaction (PCR) amplification of porcinefVIII cDNA or genomic DNA uses the human fVIII cDNA as reference (Woodet al. (1984) supra).

Porcine spleen total RNA was isolated by acid guanidiniumthiocyanate-phenol-chloroform extraction [Chomczynski et al. (1987)Anal. Biochem. 162:156–159]. Porcine cDNA was prepared from total spleenRNA using Moloney murine leukemia virus reverse transcriptase (RT) andrandom hexamers to prime the reaction (First-Strand cDNA Synthesis Kit,Pharmacia Biotech) unless otherwise indicated. RT reactions contained 45mM Tris-Cl, pH 8.3, 68 mM KCl, 15 mM DTT, 9 mM MgCl₂, 0.08 mg/ml bovineserum albumin and 1.8 mM deoxynucleotide triphosphate (dNTP). Porcinegenomic DNA was isolated from spleen using a standard procedure(Strauss, W. M. (1995) In Current Protocols in Molecular Biology, F. M.Ausubel et al., editors, John Wiley & Sons, pp. 2.2.1–2.2.3). Isolationof DNA from agarose gels was done using Geneclean II (Bio 101) or QuiexII Gel Extraction Kit (Qiagen).

PCR reactions were done using a Hybaid OmniGene thermocycler. For PCRreactions employing Taq DNA polymerase, reactions included 0.6 mM MgCl₂,0.2 mM dNTPs, 0.5 μM oligonucleotide primers, 50 U/ml polymerase and 0.1volume of first strand cDNA reaction mix. Except where indicatedotherwise, PCR products were gel purified, blunt-ended with Klenowfragment, precipitated with ethanol, and either ligated to the EcoRVsite of dephosphorylated pBluescript II KS- or ligated withphosphorylated ClaI linkers using T4 ligase, digested with ClaI,purified by Sephacryl S400 chromatography, and ligated to ClaI-cut,dephosphorylated pBluescript II KS-. Ligations were done using T4 DNAligase (Rapid DNA ligation kit, Boehringer Mannheim) except whereindicated otherwise. Insert-containing pBluescript II KS- plasmids wereused to transform E. coli Epicurean XL1-Blue cells.

Sequencing of plasmid DNA was done using an Applied Biosystems 373aautomated DNA sequencer and the PRISM dye terminator kit or manuallyusing Sequenase v. 2.0 sequencing kit (Amersham Corporation). Directsequencing of PCR products, including ³²P-end labelling ofoligonucleotides was done using a cycle sequencing protocol (dsDNA CycleSequencing System, Life Technologies).

Isolation of Porcine fVIII cDNA Clones Containing 5′ UTR Sequence,Signal Peptide and A1 Domain Codons.

The porcine fVIII cDNA 5′ to the A2 domain was amplified by nestedRT-PCR of female pig spleen total RNA using a 5′ rapid amplification ofcDNA ends (5′-RACE) protocol (Marathon cDNA Amplification, Clontech,Version PR55453). This included first strand cDNA synthesis using alock-docking oligo(dT) primer [Borson, N. D. et al. (1992) PCR MethodsAppl. 2:144–148], second strand cDNA synthesis using E. coli DNApolymerase I, and ligation with a 5′ extended double stranded adaptor,SEQ ID NO:13 5′-CTA ATA CGA CTC ACT ATA GGG CTC GAG CGG CCG CCC GGG CAGGT-3 3′-H₂N-CCCGTCCA-PO₄-5′ whose short strand was blocked at the 3′ endwith an amino group to reduce non-specific PCR priming and which wascomplementary to the 8 nucleotides at the 3′ end (Siebert, P. D., et al.(1995) Nucleic. Acids. Res. 23:1087–1088). The first round of PCR wasdone using an adaptor-specific oligonucleotide, SEQ ID NO:14 5′-CCA TCCTM TAC GAC TCA CTA TAG GGC-3′ (designated AP1) as sense primer, and aporcine fVIII A2 domain specific oligonucleotide SEQ ID NO:15 5′-CCA TTGACA TGA AGA CCG TTT CTC-3′ (nt 2081–2104) as antisense primer. Thesecond round of PCR was done using a nested, adaptor-specificoligonucleotide, SEQ ID NO:16 5′-ACT CAC TAT AGG GCT CGA GCG GC-3′(designated AP2) as sense primer, and a nested, porcine A2domain-specific oligonucleotide SEQ ID NO:17 5′-GGG TGC AAA GCG CTG ACATCA GTG-3′ (nt 1497–1520) as antisense primer. PCR was carried out usinga commercial kit (Advantage cDNA PCR core kit) which employs anantibody-mediated hot start protocol [Kellogg, D. E. et al. (1994)BioTechniques 16:1134–1137]. PCR conditions included denaturation at 94°C. for 60 sec, followed by 30 cycles (first PCR) or 25 cycles (secondPCR) of denaturation for 30 sec at 94° C., annealing for 30 sec at 60°C. and elongation for 4 min at 68° C. using tube temperature control.This procedure yielded a prominent ≈1.6 kb product which was consistentwith amplification of a fragment extending approximately 150 bp into the5′ UTR. The PCR product was cloned into pBluescript using ClaI linkers.The inserts of four clones were sequenced in both directions.

The sequence of these clones included regions corresponding to 137 bp ofthe 5′ UTR, the signal peptide, the A1 domain and part of the A2 domain.A consensus was reached in at least 3 of 4 sites. However, the clonescontained an average of 4 apparent PCR-generated mutations, presumablydue to the multiple rounds of PCR required to generate a clonableproduct. Therefore, we used sequence obtained from the signal peptideregion to design a sense strand phosphorylated PCR primer, SEQ ID NO:185′-CCT CTC GAG CCA CCA TGT CGA GCC ACC ATG CAG CTA GAG CTC TCC ACCTG-3′, designated RENEOPIGSP, for synthesis of another PCR product toconfirm the sequence and for cloning into an expression vector. Thesequence in bold represents the start codon. The sequence 5′ to thisrepresents sequence identical to that 5′ of the insertion site into themammalian expression vector ReNeo used for expression of fVIII (Lubin etal. (1994) supra). This site includes an Xho1 cleavage site(underlined). RENEOPIGSP and the nt 1497–1520 oligonucleotide were usedto prime a Taq DNA polymerase-mediated PCR reaction using porcine femalespleen cDNA as a template. DNA polymerases from several othermanufacturers failed to yield a detectable product. PCR conditionsincluded denaturation at 94° C. for four min, followed by 35 cycles ofdenaturation for 1 min at 94° C., annealing for 2 min at 55° C. andelongation for 2 min at 72° C., followed by a final elongation step for5 min at 72° C. The PCR product was cloned into pBluescript using ClaIlinkers. The inserts of two of these clones were sequenced in bothdirections and matched the consensus sequence.

Isolation of Porcine fVIII cDNA Clones Containing A3, C1 and 5′ half ofthe C2 Domain Codons.

Initially, two porcine spleen RT-PCR products, corresponding to a B-A3domain fragment (nt4519–5571) and a C1–C2 domain fragment (nt 6405–6990)were cloned. The 3′ end of the C2 domain that was obtained extended intothe exon 26 region, which is the terminal exon in fVIII. The B-A3product was made using the porcine-specific B domain primer, SEQ IDNO:19 5′ CGC GCG GCC GCG CAT CTG GCA AAG CTG AGT T 3′, where theunderlined region corresponds to a region in porcine fVIII that alignswith nt 4519–4530 in human fVIII. The 5′ region of the oligonucleotideincludes a NotI site that was originally intended for cloning purposes.The antisense primer used in generating the B-A3 product, SEQ ID NO:205′-GAA ATA AGC CCA GGC TTT GCA GTC RAA-3′ was based on the reversecomplement of the human fVIII cDNA sequence at nt 5545–5571. The PCRreaction contained 50 mM KCl, 10 mM Tris-Cl, pH 9.0, 0.1% Triton X-100,1.5 mM MgCl₂, 2.5 mM dNTPs, 20 μM primers, 25 units/ml Taq DNApolymerase and 1/20 volume of RT reaction mix. PCR conditions weredenaturation at 94° C. for 3 min, followed by 30 cycles of denaturationfor 1 min at 94° C., annealing for 2 min at 50° C. and elongation for 2min at 72° C. The PCR products were phosphorylated using T4 DNA kinaseand NotI linkers were added. After cutting with NotI, the PCR fragmentswere cloned into the NotI site of BlueScript II KS- and transformed intoXL1-Blue cells.

The C1–C2 product was made using the known human cDNA sequence tosynthesize sense and antisense primers, SEQ ID NO:21 5′-AGG AAA TTC CACTGG AAC CTT N-3′ (nt 6405–6426) and SEQ ID NO:22 5′-CTG GGG GTG AAT TCGAAG GTA GCG N-3′ (reverse complement of nt 6966–6990), respectively. PCRconditions were identical to those used to generate the B-A2 product.The resulting fragment was ligated to the pNOT cloning vector using thePrime PCR Cloner Cloning System (5 Prime-3 Prime, Inc., Boulder,Colorado) and grown in JM109 cells.

The B-A3 and C1–C2 plasmids were partially sequenced to make theporcine-specific sense and antisense oligonucleotides, SEQ ID NO:235′-GAG TTC ATC GGG MG ACC TGT TG-3′ (nt 4551–4573) and SEQ ID NO:245′-ACA GCC CAT CM CTC CAT GCG AAG-3′ (nt 6541–6564), respectively. Theseoligonucleotides were used as primers to generate a 2013 bp RT-PCRproduct using a Clontech Advantage cDNA PCR kit. This product, whichcorresponds to human nt 4551–6564, includes the region corresponding tothe light chain activation peptide (nt 5002–5124), A3 domain (nt5125–6114) and most of the C1 domain (nt 6115–6573). The sequence of theC1–C2 clone had established that human and porcine cDNAs from nt 6565 tothe 3′ end of the C1 domain were identical. The PCR product cloned intothe EcoRV site of pBluescript II KS-. Four clones were completelysequenced in both directions. A consensus was reached in at least 3 of 4sites.

Isolation of Porcine fVIII cDNA Clones Containing the 3′ Half of the C2Domain Codons.

The C2 domain of human fVIII (nucleotides 6574–7053) is contained withinexons 24–26 [Gitschier J. et al. (1984) Nature 312:326–330]. Human exon26 contains 1958 bp, corresponding nucleotides 6901–8858. It includes1478 bp of 3′ untranslated sequence. Attempts to clone the exon 26 cDNAcorresponding to the 3′ end of the C2 domain and the 3′ UTR by 3′ RACE[Siebert et al. (1995) supra], inverse PCR [Ochman, H. et al. (1990)Biotechnology (N.Y). 8:759–760], restriction site PCR [Sarkar, G. et al.(1993) PCR Meth. Appl. 2:318–322], “unpredictably primed” PCR[Dominguez, O. et al. (1994) Nucleic. Acids Res. 22:3247–3248] and byscreening a porcine liver cDNA library failed. 3′ RACE was attemptedusing the same adaptor-ligated double stranded cDNA library that wasused to successfully used to clone the 5′ end of the porcine fVIII cDNA.Thus, the failure of this method was not due to the absence of cDNAcorresponding to exon 26.

A targeted gene walking PCR procedure [Parker, J. D. et al. (1991)Nucleic. Acids. Res. 19:3055–3060] was used to clone the 3′ half of theC2 domain. A porcine-specific sense primer, SEQ ID NO:255′-TCAGGGCAATCAGGACTCC-3′ (nt 6904–6924) was synthesized based on theinitial C2 domain sequence and was used in a PCR reaction withnonspecific “walking” primers selected from oligonucleotides availablein the laboratory. The PCR products were then targeted by primerextension analysis [Parker et al. (1991) Bio Techniques 10:94–101] usinga ³²P-end labelled porcine-specific internal primer, SEQ ID NO:265′-CCGTGGTGAACGCTCTGGACC-3′ (nt 6932–6952). Interestingly, of the 40nonspecific primers tested, only two yielded positive products on primerextension analysis and these two corresponded to an exact and adegenerate human sequence at the 3′ end of the C2 domain: SEQ ID NO:275′-GTAGAGGTCCTGTGCCTCGCAGCC-3′ (nt 7030–7053) and SEQ ID NO:285′-GTAGAGSTSCTGKGCCTCRCAKCCYAG-3′, (nt 7027–7053). These primers hadinitially been designed to yield a product by conventional RT-PCR butfailed to yield sufficient product that could be visualized by ethidiumbromide dye binding. However, a PCR product could be identified by themore sensitive primer extension method. This product was gel-purifiedand directly sequenced. This extended the sequence of porcine fVIII 3′to nt 7026.

Additional sequence was obtained by primer extension analysis of anested PCR product generated using the adaptor-ligated double-strandedcDNA library used in the 5′-RACE protocol described previously. Thefirst round reaction used the porcine exact primer SEQ ID NO:295′-CTTCGCATGGAGTTGATGGGCTGT-3′ (nt 6541–6564) and the AP1 primer. Thesecond round reaction used SEQ ID NO:30 5′-AATCAGGACTCCTCCACCCCCG-3′ (nt6913–6934) and the AP2 primer. Direct PCR sequencing extended thesequence 3′ to the end of the C2 domain (nt 7053). The C2 domainsequence was unique except at nt 7045 near the 3′ end of the C2 domain.Analysis of repeated PCR reactions yielded either A, G or a double readof A/G at this site.

Sequencing was extended into the 3′ UTR using two additional primers,SEQ ID NO:31 5′-GGA TCC ACC CCA CGA GCT GG-3′ (nt 6977–6996) and SEQ IDNO:32 5′-CGC CCT GAG GCT CGA GGT TCT AGG-3′ (nt 7008–7031).Approximately 15 bp of 3′ UTR sequence were obtained, although thesequence was unclear at several sites. Several antisense primers thenwere synthesized based on the best estimates of the 3′ untranslatedsequence. These primers included the reverse complement of the TGA stopcodon at their 3′ termini. PCR products were obtained from both porcinespleen genomic DNA and porcine spleen cDNA that were visualized byagarose gel electrophoresis and ethidium bromide staining using aspecific sense primer SEQ ID NO:33 5′-AAT CAG GAC TCC TCC ACC CCC G-3′(nt 6913–6934) and the 3′ UTR antisense primer, SEQ ID NO:345′-CCTTGCAGGAATTCGATTCA-3′. To obtain sufficient quantities of materialfor cloning purposes, a second round of PCR was done using a nestedsense primer, SEQ ID NO:35 5′-CCGTGGTGAACGCTCTGGACC-3′ (nt 6932–6952)and the same antisense primer. The 141 bp PCR product was cloned intoEcoRV-cut pBluescript II KS-. Sequence of three clones derived fromgenomic DNA and three clones derived from cDNA was obtained in bothdirections. The sequence was unambiguous except at nt 7045, wheregenomic DNA was always A and cDNA was always G.

Multiple DNA Sequence Alignments of Human, Porcine, and Mouse fVIII(FIG. 1A-1H).

Alignments of the signal peptide, A1, A2, A3, C1, and C2 regions weredone using the CLUSTALW program [Thompson, J. D. et al. (1994) Nucleic.Acids. Res. 22:4673–4680]. Gap open and gap extension penalties were 10and 0.05 respectively. The alignments of the human, mouse, and pig Bdomains have been described previously [Elder et al. (1993) supra]. Thehuman A2 sequence corresponds to amino acids 373–740 in SEQ ID NO:2. Theporcine A2 amino acid sequence is given in SEQ ID NO:4, and the mouse A2domain amino acid sequence is given in SEQ ID NO:6, amino acids 392–759.

EXAMPLE 11 Expression of Active, Recombinant B-domainless Porcine FactorVIII (PB⁻

Materials

Citrated hemophilia A and normal pooled human plasmas were purchasedfrom George King Biomedical, Inc. Fetal bovine serum, geneticin,penicillin, streptomycin, DMEM/F12 medium and AIM-V medium werepurchased from Life Technologies, Inc. Taq DNA polymerase was purchasedfrom Promega. Vent DNA polymerase was purchased from New EnglandBiolabs. Pfu DNA polymerase and the phagemid pBlueScript II KS⁻ werepurchased from Stratagene. Synthetic oligonucleotides were purchasedfrom Life Technologies or Cruachem, Inc. Restriction enzymes werepurchased from New England Biolabs or Promega. 5′-phosphorylated primerswere used when PCR products were produced for cloning purposes.Nucleotide (nt) numbering of oligonucleotides used as primers forpolymerase chain reaction (PCR) amplification of porcine fVIII cDNA orgenomic DNA uses the human fVIII cDNA as reference [Wood et al. (1984)Nature 312:330–337]. A fVIII expression vector, designated HB⁻/ReNeo,was obtained from Biogen, Inc. HB⁻/ReNeo contains ampicillin andgeneticin resistance genes and a human fVIII cDNA that lacks the entireB domain, defined as the Ser741-Arg1648 cleavage fragment produced bythrombin. To simplify mutagenesis of fVIII C2 domain cDNA, which is atthe 3′ end of the fVIII insert in ReNeo, a NotI site was introduced twobases 3′ to the stop codon of HB⁻/ReNeo by splicing-by-overlap extension(SOE) mutagenesis [Horton, R. M. et al. (1993) Methods Enzymol.217:270–279]. This construct is designated HB⁻ReNeo/NotI.

Total RNA was isolated by acid guanidinium thiocyanate-phenol-chloroformextraction [Chomczynski, P. et al. (1987) Anal. Biochem. 162:156–159].cDNA was synthesized from mRNA using Moloney murine leukemia virusreverse transcriptase (RT) and random hexamers according to instructionssupplied by the manufacturer (First-Strand cDNA Synthesis Kit, PharmaciaBiotech). Plasmid DNA was purified using a Qiagen Plasmid Maxi Kit(Qiagen, Inc.). PCR reactions were done using a Hybaid OmniGenethermocycler using Taq, Vent, or Pfu DNA polymerases. PCR products weregel purified, precipitated with ethanol, and ligated into plasmid DNAusing T4 DNA ligase (Rapid DNA ligation kit, Boehringer Mannheim).Insert-containing plasmids were used to transform E. coli EpicureanXL1-Blue cells. All novel fVIII DNA sequences generated by PCR wereconfirmed by dideoxy sequencing using an Applied Biosystems 373aautomated DNA sequencer and the PRISM dye terminator kit.

Construction of a Hybrid fVIII Expression Vector, HP20, Containing thePorcine C2 Domain.

A porcine fVIII cDNA corresponding to the 3′ end of the C1 domain andall of the C2 domain was cloned into pBluescript by RT-PCR from spleentotal RNA using primers based on known porcine fVIII cDNA sequence[Healy, J. F. et al. (1996) Blood 88:4209–4214]. This construct andHB⁻/ReNeo were used as templates to construct a human C1-porcine C2fusion product in pBlueScript by SOE mutagenesis. The C1–C2 fragment inthis plasmid was removed with ApaI and NotI and ligated intoApaI/NotI-cut HB⁻/ReNeo/NotI to produce HP20/ReNeo/NotI.

Construction of B-domain Deleted Hybrid Human/Porcine fVIII Containingthe Porcine Light Chain (HP18)

The human fVIII light chain consists of amino acid residuesAsp1649-Tyr2332. The corresponding residues in the porcine fVIII cDNAwere substituted for this region of HB⁻ to produce a hybridhuman/porcine fVIII molecule designated HP18. This was done bysubstituting a PCR product corresponding to porcine A2 region, the A3domain, the C1 domain, and part of the C2 domain for the correspondingregion in HP20. To facilitate constructions, a synonymous AvrII site wasintroduced into nt 2273 at the junction of the A2 and A3 domains of HP20by SOE mutagenesis.

Construction of B-domain Deleted Hybrid Human/Porcine fVIII Containingthe Porcine Signal Peptide, A1 Domain and A2 Domain (HP22)

The human fVIII signal peptide, A1 domain and A2 domains consist ofamino acid residues Met(-19)-Arg740. The corresponding residues in theporcine fVIII cDNA were substituted for this region of HB⁻ to produce amolecule designated HP22. Additionally, a synonymous AvrII site wasintroduced into nt 2273 at the junction of the A2 and A3 domains of HP22by SOE mutagenesis. HP22 was constructed by fusion of a porcine signalpeptide-A1-partial A2 fragment in pBlueScript [Healy et al. (1996)supra] with a B-domainless hybrid human/porcine fVIII containing theporcine A2 domain, designated HP1 [Lubin et al. (1994) supra].

Construction of Porcine B Domainless fVIII-(PB⁻)

A SpeI/NotI fragment of HP18/BS (+AvrII) was digested with AvrII/NotIand ligated into AvrII/NotI-digested HP22/BS (+AvrII) to produce aconstruct PB⁻/BS (+AvrII), which consists of the porcine fVIII lackingthe entire B domain. PB-was cloned into ReNeo by ligating an XbaI/NotIfragment of PB⁻/BS (+AvrII) into HP22/ReNeo/NotI (+AvrII).

Expression of Recombinant fVIII Molecules

PB⁻/ReNeo/NotI (+AvrII) and HP22/ReNeo/NotI (+AvrII) were transientlytransfected into COS cells and expressed as described previously [Lubin,I. M. et al. (1994) J. Biol. Chem. 269:8639–8641]. HB⁻/ReNeo/NotI and noDNA (mock) were transfected as a control.

The fVIII activity of PB⁻, HP22, and HB⁻ were measured by a chromogenicassay as follows. Samples of fVIII in COS cell culture supernatants wereactivated by 40 nM thrombin in a 0.15 M NaCl, 20 mM HEPES, 5 mM CaCl₂,0.01% Tween-80, pH 7.4 in the presence of 10 nM factor IXa, 425 nMfactor X, and 50 μM unilamellar phosphatidylserine-[phosphatidycholine(25/75 w/w) vesicles. After 5 min, the reaction was stopped with 0.05 MEDTA and 100 nM recombinant desulfatohirudin and the resultant factor Xawas measured by chromogenic substrate assay. In the chromogenicsubstrate assay, 0.4 mM Spectrozyme Xa was added and the rate ofpara-nitroanilide release was measured by measuring the absorbance ofthe solution at 405 nm.

Results of independently transfected duplicate cell culture supernatants(absorbance at 405 nm per minute)

HB⁻: 13.9

PB⁻: 139

HP22: 100

mock: <0.2

These results indicate that porcine B-domainless fVIII and aB-domainless fVIII consisting of the porcine A1 and A2 subunits areactive and suggest that they have superior activity to humanB-domainless fVIII.

PB⁻ was partially purified and concentrated from the growth medium byheparin-Sepharose chromatography. Heparin-Sepharose (10 ml) wasequilibrated with 0.075 M NaCl, 10 mM HEPES, 2.5 mM CaCl₂, 0.005%Tween-80, 0.02% sodium azide, pH 7.40. Medium (100–200 ml) fromexpressing cells was applied to the heparin-Sepharose, which then waswashed with 30 ml of equilibration buffer without sodium azide. PB⁻ waseluted with 0.65 M NaCl, 20 mM HEPES, 5 mM CaCl₂, 0.01% Tween-80, pH7.40 and was stored at −80° C. The yield of fVIII coagulant activity wastypically 50–75%.

Stable Expression of Porcine B-domainless fVIII (PB⁻)

Transfected cell lines were maintained in Dulbecco's modified Eagle'smedium-F12 containing 10% fetal bovine serum, 50 U/ml penicillin, 50μg/ml streptomycin. Fetal bovine serum was heat inactivated at 50° C.for one hour before use. HB⁻/ReNeo and PB⁻ReNeo/NotI (+AvrII) werestably transfected into BHK cells and selected for geneticin resistanceusing a general protocol that has been described previously [Lubin etal. (1994) Biol. Chem. 269:8639–8641] except that expressing cells weremaintained in growth medium containing 600 μg/ml geneticin. Cells fromCorning T-75 flasks grown to confluence were transferred to Nunc tripleflasks in medium containing 600 μg/ml geneticin and grown to confluence.The medium was removed and replaced with serum-free, AIM-V medium (LifeTechnologies, Inc.) without geneticin. Factor VIII expression wasmonitored by one-stage factor VIII coagulant activity (vide supra) and100–150 ml of medium was collected once daily for four to five days.Maximum expression levels in medium for HB⁻ and PB⁻ were 1–2 units perml and 10–12 units per ml of factor VIII coagulant activity,respectively.

Purification of PB⁻

PB⁻ was precipitated from culture supernatant using 60% saturatedammonium sulfate and then purified by W3-3 immunoaffinity chromatographyand mono Q high pressure liquid chromatography as described previouslyfor the purification of plasma-derived porcine factor VIII [Lollar etal. (1993) Factor VIII/factor VIIIa. Methods Enzymol. 222:128–143]. Thespecific coagulant activity of PB⁻ was measured by a one-stagecoagulation assay [Lollar et al. (1993) supra] and was similar toplasma-derived porcine factor VIII.

When analyzed by SDS-polyacrylamide gel electrophoresis, the PB⁻preparation contained three bands of apparent molecular masses 160 kDa,82 kDa, and 76 kDa. The 82 kDa and 76 kDa bands have been previouslydescribed as heterodimer containing the A1–A2 and ap-A3-CI-C2 domains(where ap refers to an activation peptide) [Toole et al. (1984) Nature312:342–347]. The 160 kDa band was transferred to a polyvinylidenefluoride membrane and subjected to NH2-terminal sequencing, whichyielded Arg-IIe-Xx-Xx-Tyr (where Xx represents undermined) which is theNH2-terminal sequence of single chain factor VIII [Toole et al. (1984)supra]. Thus, PB⁻ is partially processed by cleavage between the A2 andA3 domains, such that it consists of two forms, a single chainA1–A2-ap-A3-CI-C2 protein and a A1–A2/ap-A3-CI-C2 heterodimer. Similarprocessing of recombinant HB⁻ has been reported [Lind et al. (1995) Eur.J. Biochem. 232:19–27].

Characterization of Porcine Factor VIII

We have determined the cDNA sequence of porcine fVIII corresponding to137 bp of the 5′ UTR, the signal peptide coding region (57 bp), and theA1 (1119 bp), A3 (990 bp), C1 (456 bp), and C2 (483 bp) domains. Alongwith previously published sequence of the B domain and light chainactivation peptide regions [Toole et al. (1986) supra] and the A2 domain[Lubin et al. (1994) supra], the sequence reported here completes thedetermination of the porcine fVIII cDNA corresponding to the translatedproduct. A fragment that included the 5′ UTR region, signal peptide, andA1 domain cDNA was cloned using a 5′-RACE RT-PCR protocol. A primerbased on human C2 sequence was successful in producing an RT-PCR productthat led to cloning of the A3, C1, and 5′ half of the C2 domain. ThecDNA corresponding to the 3′ half of the C2 domain and 3′ UTR cDNAproved difficult to clone. The remainder of the C2 domain ultimately wascloned by a targeted gene walking PCR procedure [Parker et al. (1991)supra].

The sequence reported herein SEQ ID NO:36 was unambiguous except at nt7045 near the 3′ end of the C2 domain, which is either A or G asdescribed hereinabove. The corresponding codon is GAC (Asp) or AAC(Asn). The human and mouse codons are GAC and CAG (GIn), respectively.Whether this represents a polymorphism or a reproducible PCR artifact isunknown. Recombinant hybrid human/porcine B-domainless fVIII cDNAscontaining porcine C2 domain substitutions corresponding to both the GACand AAC codons have been stably expressed with no detectable differencein procoagulant activity. This indicates that there is not a functionaldifference between these two C2 domain variants.

The alignment of the predicted amino acid sequence of full-lengthporcine fVIII SEQ ID NO:37 with the published human [Wood et al. (1984)supra] and murine [Elder et al. (1993) supra] sequences is shown in FIG.1A-1H along with sites for post-translational modification, proteolyticcleavage, and recognition by other macromolecules. The degree ofidentity of the aligned sequences is shown in Table VII. As notedpreviously, the B domains of these species are more divergent than the Aor C domains. This is consistent with the observation that the B domainhas no known function, despite its large size [Elder et al. (1993)supra; Toole et al. (1986) supra]. The results of the present inventionconfirm that the B domain or porcine fVIII is not necessary foractivity. Based on the sequence data presented herein, porcine fVIIIhaving all or part of the B-domain deleted can be synthesized byexpressing the porcine fVIII coding DNA having deleted therefrom all orpart of codons of the porcine B domain. There is also more divergence ofsequences corresponding to the A1 domain APC/factor IXa cleavage peptide(residues 337–372) and the light chain activation peptide (Table VII).The thrombin cleavage site at position 336 to generate the 337–372peptide is apparently lost in the mouse since this residue is glutamineinstead of arginine [Elder et al. (1993) supra]. The relatively rapiddivergence of thrombin cleavage peptides (or in mouse fVIII a possiblyvestigial 337–372 activation peptide) has been previously noted for thefibrinopeptides [Creighton, T. E. (1993) In Proteins: Structures andMolecular Properties, W. H. Freeman, New York, pp. 105–138]. Lack ofbiological function of these peptides once cleaved has been cited as apossible reason for the rapid divergence. Arg562 in human fVIII has beenproposed to be the more important cleavage site for activated protein Cduring the inactivation of fVIII and fVIIIa [Fay, P. J. et al. (1991) J.Biol. Chem. 266:20139–20145]. This site is conserved in human, porcineand mouse fVIII.

Potential N-linked glycosylation sites are also shown in bold in FIG.1A-1H. There are eight conserved N-linked glycosylation sites: one inthe A1 domain, one in the A2 domain, four in the B domain, one in the A3domain, and one in the C1 domain. The 19 A and C domain cysteines areconserved, whereas there is divergence of B domain cysteines. Six of theseven disulfide linkages in fVIII are found at homologous sites infactor V and ceruloplasmin, and both C domain disulfide linkages arefound in factor V [McMullen, B. A. et al. (1995) Protein Sci.4:740–746]. Human fVIII contains sulfated tyrosines at positions 346,718, 719, 723, 1664, and 1680 [Pittman, D. D. et al. (1992) Biochemistry31:3315–3325; Michnick, D. A. et al. (1994) J. Biol. Chem.269:20095–20102]. These residues are conserved in mouse fVIII andporcine fVIII (FIG. 1), although the CLUSTALW program failed to alignthe mouse tyrosine corresponding to Tyr346 in human fVIII.

Mouse and pig plasma can correct the clotting defect in human hemophiliaA plasma, which is consistent with the level of conservation of residuesin the A and C domains of these species. The procoagulant activity ofporcine fVIII is superior to that of human fVIII [Lollar, P. et al.(1992) J. Biol. Chem. 267:23652–23657]. The recombinant porcine factorVIII (B domain-deleted) expressed and purified as herein described alsodisplays greater specific coagulant activity than human fVIII, beingcomparable to plasma-derived porcine fVIII. This may be due to adecreased spontaneous dissociation rate of the A2 subunit from theactive A1/A2/A3-C1–C2 fVIIIa heterotrimer. Whether this difference inprocoagulant activity reflects an evolutionary change in function as anexample of species adaptation [Perutz, M. F. (1996) Adv. Protein Chem.36:213–244] is unknown. Now that the porcine fVIII cDNA sequencecorresponding to the translated product is complete, homolog scanningmutagenesis [Cunningham, B. C., et al. (1989) Science 243:1330–1336] mayprovide a way to identify structural differences between human andporcine fVIII that are responsible for the superior activity of thelatter.

Porcine fVIII is typically less reactive with inhibitory antibodies thatarise in hemophiliacs who have been transfused with fVIII or which ariseas autoantibodies in the general population. This is the basis for usingporcine fVIII concentrate in the management of patients with inhibitoryantibodies [Hay and Lozier (1995) supra]. Most inhibitors are directedagainst epitopes located in the A2 domain or C2 domain [Fulcher, C. A.et al. (1985) Proc. Natl. Acad. Sci. USA 82:7728–7732; Scandella, D. etal. (1988) Proc. Natl. Acad. Sci. USA 85:6152–6156; Scandella, D. et al.(1989) Blood 74:1618–1626]. Additionally, an epitope of unknownsignificance has been identified that is in either the A3 or C1 domain[Scandella et al. (1989) supra; Scandella, D. et al. (1993) Blood82:1767–1775; Nakai, H. et al. (1994) Blood 84:224a]. The A2 epitope hasbeen mapped to residues 484–508 by homolog scanning mutagenesis [Healeyet al. (1995) supra]. In this 25 residue segment, there is relativelylow proportion of identical sequence (16/25 or 64%). It is interestingthat this region, which appears to be functionally important based onthe fact that antibodies to it are inhibitory, apparently has beensubjected to relatively more rapid genetic drift. Alignment of theporcine A2 domain and A3 domains indicate that the A2 epitope shares nodetectable homology with the corresponding region in the A3 domain.

The C2 inhibitor epitope of human fVIII has been proposed to be locatedto within residues 2248–2312 by deletion mapping [Scandella, D. et al.(1995) Blood 86:1811–1819]. Human and porcine fVIII are 83% identical inthis 65 residue segment. However, homolog scanning mutagenesis of thisregion to characterize the C2 epitope has revealed that a majordeterminant of the C2 epitope was unexpectedly located in the regioncorresponding to human amino acids 2181–2243 (SEQ ID NO:2) and FIG. 1H.

Human-porcine hybrid factor VIII proteins were made in which variousportions of the C2 domain of human factor VIII were replaced by thecorresponding portions of porcine factor VIII, using the strategy hereindescribed (Example 8). The synthesis of the various C2-hybrid factorVIIIs was accomplished by constructing hybrid coding DNA, using thenucleotide sequence encoding the porcine C2 region given in SEQ IDNO.37. Each hybrid DNA was expressed in transfected cells, such that thehybrid factor VIIIs could be partially purified from the growth medium.Activity, in the absence of any inhibitor, was measured by the one-stageclotting assay.

A battery of five human inhibitors was used to test each hybrid factorVIII. The inhibitor plasmas containing anti factor VIII antibody hadbeen previously shown to be directed against human C2 domain, based onthe ability of recombinant human C2 domain to neutralize the inhibition.In all the test plasmas, the inhibitor titer was neutralized greaterthan 79% by C2 domain or light chain but less than 10% by recombinanthuman A2 domain. In addition the C2-hybrid factor VIIIs were testedagainst a murine monoclonal antibody, which binds the C2 domain, andlike human C2 inhibitor antibodies, it inhibited the binding of factorVIII to phospholipid and to von Willebrand factor.

By comparing the antibody inhibitor titers against the C2-hybrid factorVIIIs, the major determinant of the human C2 inhibitor epitope was shownto be the region of residues 2181–2243 (SEQ ID NO:2, see also FIG. 1H).Anti-C2 antibodies directed to a region COOH-terminal to residue 2253were not identified in four of the five patient sera. In comparinghybrids having porcine sequence corresponding to human amino acidresidues numbers 2181–2199 and 2207–2243, it was apparent that bothregions contribute to antibody binding. The porcine amino acid sequencecorresponding to human residues 2181–2243 is numbered 1982–2044 in SEQID NO:37. The sequence of porcine DNA encoding porcine amino acidsnumbered 1982–2044 is nucleotides numbered 5944–6132 in SEQ ID NO:35.

Referring to FIG. 1H, it can be seen that in the region 2181–2243, thereare 16 amino acid differences between the human and porcine sequences.The differences are found at residues 2181, 2182, 2188, 2195–2197, 2199,2207, 2216, 2222, 2224, 2227, 2234, 2238 and 2243. Amino acidreplacement at one or more of these numbered residues can be carried outto make a modified human factor VIII non-reactive to human anti-C2inhibitor antibodies. Alanine scanning mutagenesis provides a convenientmethod for generating alanine substitutions for naturally-occurringresidues, as previously described. Amino acids other than alanine can besubstituted as well, as described herein. Alanine substitutions forindividual amino acids, especially those which are non-identical betweenhuman/porcine or human/mouse or which are most likely to contribute toantibody binding, can yield a modified factor VIII with reducedreactivity to inhibitory antibodies.

In addition, the strategy of inserting amino acids with lower potentialto be immunogenic in the defined region of residues 2181–2243 yieldsmodified factor VIIIs having reduced immunogenicity. Reducedimmunogenicity factor VIII is useful as a factor VIII supplement fortreatment of hemophilia A patients in preference to natural-sequencefactor VIII. Patients treated with reduced immunogenicity factor VIIIare less likely to develop inhibitory antibodies, and are therefore lesslikely to suffer from reduced effectiveness of treatment over theirlifetimes.

FIGS. 1A–1H taken together provide an aligned sequence comparison of thehuman, pig and mouse factor VIII amino acid sequences. FIG. 1A comparessignal peptide regions (human, SEQ ID NO:40; porcine, SEQ ID NO:37,amino acids 1–19; murine, SEQ ID NO:6, amino acids 1–19). Note that theamino acids in FIG. 1A-1H are numbered at the first Alanine of themature protein as number 1, with amino acids of the signal peptideassigned negative numbers. The Human fVIII sequence in SEQ ID NO:2 alsobegins with the first Alanine of the mature protein as amino acidnumber 1. In the amino acid sequences of mouse fVIII (SEQ ID NO:6) andporcine fVIII (SEQ ID No:37), the first amino acid (alanine) of themature sequence is amino acid number 20. FIG. 1A-1H shows an alignmentof the corresponding sequences of human, mouse and pig fVIII, such thatthe regions of greatest amino acid identity are juxtaposed. The aminoacid numbers in FIG. 1A-1H apply to human fVIII only. FIG. 1B gives theamino acid sequences for the A1 domain of human (SEQ ID NO:2, aminoacids 1–372), porcine (SEQ ID NO:37, amino acids 20–391), and murine(SEQ ID NO:6, amino acids 20–391). FIG. 1C provides amino acid sequencesfor the Factor VIII A2 domains from human (SEQ ID NO:2, amino acids373–740), pig (SEQ ID NO:37, amino acids 392–759) and mouse (SEQ IDNO:6, amino acids 392–759). FIG. 1D provides the amino acid sequences ofB domains of human factor VIII (SEQ ID NO:2, amino acids 741–1648), pig(SEQ ID NO:37, amino acids 760–1449) and mouse (SEQ ID NO:6, amino acids760–1640). FIG. 1E compares the amino acid sequences of Factor VIIIlight chain activation peptides of human, pig and mouse (SEQ ID NO:2,amino acids 1649–1689; SEQ ID NO:37, amino acids 1450–1490; and SEQ IDNO:6, amino acids 1641–1678, respectively). FIG. 1F provides thesequence comparison for human, pig and mouse Factor VIII A3 domains (SEQID NO:2, amino acids 1690–2019; SEQ ID NO:37, amino acids 1491–1820; andSEQ ID NO:6, amino acids 1679–2006, respectively. FIG. 1G provides theamino acid sequences of the Factor VIII C1 domains of human, pig andmouse (SEQ ID NO:2, amino acids 2020–2172; SEQ ID NO:37, amino acids1821–1973; and SEQ ID NO:6, amino acids 2007–2159, respectively). FIG.1H provides sequence data for the C2 domains of the Factor VIII C2domains of human, pig and mouse (SEQ ID NO:2, amino acids 2173–2332; SEQID NO:37, amino acids 1974–2133; and SEQ ID NO:6, amino acids2160–2319,respectively).

The diamonds represent tyrosine sulfation sites, potential glycosylationsites are in bold type, proposed binding sites for Factor IXa,phospholipid and Protein C are double-underlined, and regions involvedin binding anti-A2 and anti-C2 inhibitory antibodies are italicized.Asterisks highlight amino acid sequences which are conserved. See alsoSEQ ID NO:36 (porcine factor VIII cDNA) and SEQ ID NO:37 (deduced aminoacid sequence of porcine factor VIII). The human numbering system isused as the reference [Wood et al. (1984) supra]. The A1, A2, and Bdomains are defined by thrombin cleavage sites at positions 372 and 740and an unknown protease cleavage site at 1648 as residues 1–372,373–740, and 741–1648, respectively [Eaton, D. L. et al. (1986)Biochemistry 25:8343–8347]. The A3, C1, and C2 domains are defined asresidues 1690–2019, 2020–2172, and 2173–2332, respectively [Vehar et al.(1984) supra]. Cleavage sites for thrombin (factor IIa), factor IXa,factor Xa and APC [Fay et al. (1991) supra; Eaton, D. et al. (1986)Biochemistry 25:505–512; Lamphear, B. J. et al. (1992)Blood80:3120–3128] are shown by placing the enzyme name over thereactive arginine. An acidic peptide is cleaved from the fVIII lightchain by thrombin or factor Xa at position 1689. Proposed binding sitesfor factor IXa [Fay, P. J. et al. (1994) J. Biol. Chem. 269:20522–20527;Lenting, P. J. et al. (1994) J. Biol. Chem. 269:7150–7155), phospholipid(Foster, P. A. et al. (1990) Blood 75:1999–2004) and protein C (Walker,F. J. et al. (1990) J. Biol. Chem. 265:1484–1489] are doubly underlined.Regions involved in binding anti-A2 [Lubin et al. (1994) supra; Healeyet al. (1995) supra]; and previously proposed for anti-C2 inhibitoryantibodies are italicized. The C2 inhibitor epitope identified as hereindescribed (human amino acids 2181–2243) is shown by a single underlinein FIG. 1H. Tyrosine sulfation sites [Pittman et al. (1992) supra;Michnick et al. (1994) supra] are shown by ♦. Recognition sequences forpotential N-linked glycosylation (NXS/T, where X is not proline) areshown in bold.

The nucleotide sequence encoding the factor VIII protein lacking the Bdomain is given in SEQ ID NO:38, and the corresponding deduced aminoacid sequence is provided in SEQ ID NO:39.

1. A human factor VIII modified to comprise at least one amino acidsubstitution in the C2 domain wherein the substitution is limited to atleast one position selected from the group consisting of 2181, 2182,2195, 2196, 2197, 2207, 2216, 2222, 2224, 2225, 2226, 2228, 2234, 2238,and 2243 according to SEQ ID NO: 2, said substitution being insertion ofan immunoreactivity-reducing amino acid for the naturally-occurringamino acid, wherein the immunoreactivity-reducing amino acid is selectedfrom the group consisting of alanine, methionine, leucine, serine andglycine, said factor VIII having procoagulant activity.
 2. The factorVIII of claim 1 wherein the at least one amino acid substitution is madeat a position selected from the group consisting of 2181, 2195, 2196,2207, 2226, 2228, and
 2234. 3. The human factor VIII of claim 1 whichlacks the B domain or a part thereof.
 4. A method for modifying humanfactor VIII such that reactivity to an inhibitory antibody is reducedand procoagulant activity is retained, comprising substituting animmunoreactivity-reducing amino acid for the naturally-occurring aminoacid at at least one position in the C2 domain of human factor VIII,wherein the substitution is limited to at least one position selectedfrom the group consisting of 2181, 2182, 2195, 2196, 2197, 2207, 2216,2222, 2224, 2225, 2226, 2228, 2234, 2238, and 2243 according to SEQ IDNO: 2 and the immunoreactivity-reducing amino acid is selected from thegroup consisting of alanine, methionine, leucine, serine and glycine. 5.The method of claim 4 wherein the modified human factor VIII is made byexpressing DNA encoding human factor VIII, the DNA having at least onecodon modified to encode the amino acid substitution wherein thesubstitution is limited to at least one position selected from the groupconsisting of 2181, 2182, 2195, 2196, 2197, 2207, 2216, 2222, 2224,2225, 2226, 2228, 2234, 2238, and 2243 according to SEQ ID NO:2.
 6. Themethod of claim 4 wherein the immunoreactivity reducing amino acid isalanine.